How to make a column for an ack with a known group

You need a template for the cell, in src/argus/htmx/templates/htmx/incidents/_incident_ack_by_group.html:

{% load argus_htmx %}
{% if incident|is_acked_by:column.context.group %}X{% endif %}

You also need to add the column to the column config:

INCIDENT_TABLE_COLUMNS = [
    ..
    IncidentTableColumn(
        "mygroup_ack",
        "MYGROUP",
        "htmx/incidents/_incident_ack_by_group.html",
        context={"group": "MYGROUP"},
    )
    ..
]