Hi,
had a use case where we added bunch of activity types and we need to edit timeline to display it and to be able to filter by it.

Unfortunately, Email, Task and Call are hardcoded in angular modules, and to do this you need to few things...

First is ofcourse you need to replace Activity object in your package, save, unchek checkbox for timeline, save and then check again so Timeline addon for activity is appeared in your package.

Now you need to add all types into metadata:

+ = MetaData.Schema.AD4.TimelineEntityValues[{
    "TypeColumnValue": "e0e9040d-d6dd-4953-9012-37c1973989cb",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUOnlineBanking",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "db50ad50-11b2-42c0-aebd-73a2cefebb13",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUVMSInteractions",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "b51b6a55-d772-41ec-9a58-2c843c706c6e",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUMeridianLinkHSA",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "b2322197-9f30-4c21-bc5d-52aa0e2c71d3",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUBranchVisits",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "9d443895-83f0-4970-8647-77bc4f70fb42",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUCalls",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "5780bae4-8269-4f1b-8609-bf57b71a60f9",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUWebTracking",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "499ada64-ea13-4b18-8b84-1647ee45d3a0",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUMeridianLinkPreApproval",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "39d61345-5c91-4b0f-ac27-f7623b0311f7",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUVirtualMeeting",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "24b6d2fd-a3e9-461a-b261-9f3b427745a5",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUEmails",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "0e0da64d-16b9-4b66-9c07-336750dfe7be",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUChat",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "0c81ebf9-d460-4120-a2ad-18ccf13496c9",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUDirectMail",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}, {
    "TypeColumnValue": "03bd74ff-9622-49a3-85c0-72d7072d5270",
    "IsDefault": true,
    "ComparisonType": 3,
    "TileName": "ECUSMS",
    "SortColumn": null,
    "OwnerColumn": "Owner",
    "IconId": null,
    "ColumnLayouts": [{
        "ColumnName": "Title",
        "ColumnLayout": null
    }, {
        "ColumnName": "Status",
        "ColumnLayout": "{\"column\": 1,\"row\": 1,\"colSpan\": 6,\"rowSpan\": 1}"
    }, {
        "ColumnName": "DetailedResult",
        "ColumnLayout": "{\"column\": 1,\"row\": 2,\"colSpan\": 6,\"rowSpan\": 1}"
    }]
}]

in my case i removed OOB types email, call and task and kept only custom, layout i kept the same as OOB task but you can adjust.

here two important properties:
"TypeColumnValue": id of you activity type
"TileName": thats a name of this type.

Important that for all except that 3 hardcoded values: there should be an object with this name.
So you would need to create virtual object for all you type...

Now, moving forward, object name and primary display valule should match. And in my case i have types containing two words, and anyway creating an object with no prefix is not ideal.
My point is that if I have type "Domestic" with one word, I could create object with name "Domestic" and thats it. But this is not always work and not ideal.

So in my case I went with ECUDirectMail, but as I said, now it has to be matching with primary display column value.
So final touches:

Add column "Code" to ActivityType lookup. Fill it with "ECUDirectMail" type values. Make it primary display column value.
In the activity page: change the value what is displaying for the field, dont show default display but show custom one. In my case thats "Name".

define("ECUActivityInteraction_FormPage", /**SCHEMA_DEPS*/[]/**SCHEMA_DEPS*/, function/**SCHEMA_ARGS*/()/**SCHEMA_ARGS*/ {
	return {
		viewConfigDiff: /**SCHEMA_VIEW_CONFIG_DIFF*/[			
			{
				"operation": "insert",
				"name": "Type",
				"values": {
					"layoutConfig": {
						"column": 1,
						"row": 2,
						"colSpan": 1,
						"rowSpan": 1
					},
					"type": "crt.ComboBox",
					"label": "#ResourceString(Type_label)#",
					"labelPosition": "auto",
					"control": "$ActivityDS_Type",
					"listActions": [],
					"showValueAsLink": true,
					"controlActions": [],
					"visible": true,
					"readonly": false,
					"placeholder": "",
					"tooltip": "",
					"mode": "List"
				},
				"parentName": "SideAreaProfileContainer",
				"propertyName": "items",
				"index": 1
			}
		]/**SCHEMA_VIEW_CONFIG_DIFF*/,
		viewModelConfigDiff: /**SCHEMA_VIEW_MODEL_CONFIG_DIFF*/[
			{
				"operation": "merge",
				"path": [
					"attributes"
				],
				"values": {					
					"ActivityDS_Type": {
						"modelConfig": {
							"path": "ActivityDS.Type"
						}
					},					
					"Type_DisplayValue": {
						"modelConfig": {
							"path": "ActivityDS.TypeName"
						}
					},
					"ActivityDS_Type_List": {
						"viewModelConfig": {
							"attributes": {
								"value": {
									"modelConfig": {
										"path": "ActivityDS_Type_List_DS.Id"
									}
								},
								"displayValue": {
									"modelConfig": {
										"path": "ActivityDS_Type_List_DS.Name"
									}
								}
							}
						}
					}
				}
			}
		]/**SCHEMA_VIEW_MODEL_CONFIG_DIFF*/,
		modelConfigDiff: /**SCHEMA_MODEL_CONFIG_DIFF*/[
			{
				"operation": "merge",
				"path": [],
				"values": {
					"primaryDataSourceName": "ActivityDS"
				}
			},
			{
				"operation": "merge",
				"path": [
					"dataSources"
				],
				"values": {
					"ActivityDS": {
						"type": "crt.EntityDataSource",
						"scope": "page",
						"config": {
							"entitySchemaName": "Activity",
							"attributes": {
								"TypeName": {
									"path": "Type.Name",
									"type": "ForwardReference"
								}
							}
						}
					},
					"ActivityDS_Type_List_DS": {
						"type": "crt.EntityDataSource",
						"config": {
							"entitySchemaName": "ActivityType",
							"attributes": {
								"Name": {
									"path": "Name"
								},
								"Code": {
									"path": "Code"
								}
							}
						},
						"scope": "page"
					}
				}
			}
		]/**SCHEMA_MODEL_CONFIG_DIFF*/,
		handlers: /**SCHEMA_HANDLERS*/[
			{
				request: "crt.HandleViewModelAttributeChangeRequest",
				handler: async (request, next) => {				
					if (request.attributeName === "Type_DisplayValue" ) {						
						const type = await request.$context.ActivityDS_Type;
						const displayTypeValue = await request.$context.Type_DisplayValue;
						if (type && displayTypeValue !== type.displayValue) { 
							newValue = {...type, displayValue:displayTypeValue }; 
							request.$context.ActivityDS_Type = newValue;
						}
					}
					return next?.handle(request);
				}
			}
		]/**SCHEMA_HANDLERS*/,
		converters: /**SCHEMA_CONVERTERS*/{}/**SCHEMA_CONVERTERS*/,
		validators: /**SCHEMA_VALIDATORS*/{}/**SCHEMA_VALIDATORS*/
	};
});

and the result

note: if you change metadata of timeline addon, you will need to re-add timeline control to your page to apply changes.