deactivate Upgrade pop-up for users

OK, we use the last 2019 non-subscription version and suddenly notice a pop-up for the users which refer to an upgrade.

Of course the users can't do it since this is an enterprise environment with centrally controlled roll-out.

I wonder how this is triggered and how it can be deactivated.

There is no autostart entry and no task-scheduler-entry not is there an check-for-updates option on the users side (which is ok)

We just need to get rid of it.