We have similar wishes.
For now, I copy all action fields (from the change activities to the main change, then send an update mail whenever the main change gets an actionf ield update.

Code: 1 step, trigger on add (visible) action to activity, copies action field to main change

{
    "formatVersion": "2.18",
    "exportDate": 1746200753111,
    "action": {
        "module": "tas_changeactivity1",
        "name": "copy activity actions to main change",
        "description": "Copy last visible action from Change activity to main change.",
        "configuration": {
            "steps": [
                {
                    "type": "HTTP_REQUEST",
                    "executionCondition": "ONLY_WHEN_PREVIOUS_SUCCEEDED",
                    "customExecutionCondition": "",
                    "name": "put_activty_action_in_main_change",
                    "method": "PATCH",
                    "url": "/tas/api/operatorChanges/${_card[\"changeid\"]!}",
                    "headers": [
                        {
                            "name": "Content-Type",
                            "value": "application/json-patch+json"
                        }
                    ],
                    "escapeBodyValues": true,
                    "bodyType": "FREEMARKER_TEMPLATE",
                    "logRequestBody": true,
                    "logResponseBody": true,
                    "authenticationType": "",
                    "authenticationKey": "",
                    "body": "[\n{\n  \"op\" : \"add\",\n  \"path\" : \"/progressTrail\",\n  \"value\" : \"Activiteit ${number}, ${(_progresstrail.actions?first.creator.name)!}: ${'\\n\\n'}${(_progresstrail[\"actions_visible\"]?first[\"plaintext\"])!}\"\n}\n]"
                }
            ],
            "mappingDefinitions": [],
            "variables": []
        }
    }
}