Thanks for your reply.
I would be very happy about a rails console command to copy user preferences. I absolutely understand the design choice that user preferences prime over site settings. But the problem is that sites are evolving and their organization with it.
In our case, we switched from an organization where all announcements are posted as a new topic: the result was a huge amount of undiscussed topics (1 post only) on the front-page. I now see that I started looking into that case in Feb 2023 Unlist or archive a post when it has no reply per category.
As these announcements are relevant and containing deadlines, it was not a choice to hide them from the front-page. So we moved to an organization with 5 dedicated topics (type of announcement) in which each post is a new announcement.[1] Still as these posts are important, we tried to set the category to watched in order to get users notified in real time.
This was the beginning of the situation which resulted currently in nobody getting anything except user_mentioned and digest. The switch would have been so much easier if one could just reset all user preferences to the new site defaults. Or, as another idea, copy the user preferences of a virtual new signup to all other users.[2]
Meanwhile, I told the users about the fact that systems sometimes don’t work as intended and that notification emails won’t come for an undefined period of time.