Welcome to Meta @pkoevesdi
It isn’t possible to force users to un-watch a category easily out of the box.
If you wanted to ‘force’ all users to watch a category there is the default categories watching
site setting. If you wanted to ‘force’ all users in a group there is discourse.example.com/g/your-group-name/manage/categories
and you can change what categories you want those group members to watch.
However, members could change these whenever so if you wanted to ensure they always watched the correct categories you would have to keep going back to those settings and changing them to reset the users watched preferences and make them follow the category again.
Another way is to hide the watching, tracking, normal etc… buttons on the site and hiding the preferences/tracking user preferences using CSS. There is a guide on how you can customise your site below
However, a caveat is that any computer savvy user can bypass such customisations if they wanted for example the use of safe mode.