Add an option to remove a group but keep members in a group conversation

I love the new possibility of having a group conversations members updated automaticly when a new member is added to a nextcloud usergroup. It makes it a lot easier to keep conversations up to date. Nevertheless I am facing a problem that makes it difficult for me and my colleges to deal with the groupfeature of nextcloud talk now:

Description of the problem
In almost every educational scenario we are dealing with dynamic usergroups that get frequently updated once a year when the students change the grade. For example todays class 06a (usergroup) consists of the studens of last years 05a and so on.

Therefore it woud be benificial to have a possibility to add the students (users) only and not the dynamical changing group itself.
Otherwise all classconversaions including the associated shared files of the conversation will be automaticly passed to the new students when changing from grade 5 to grade 6 which is problematic. (same group but different sudents)
It would be great to have an option of having the conversation stop syncing the users at a certain point - like removing the group but keeping the users.
In an office scenario I could imagine a very similar situation if you add two teams to a project but once the project has started you don't want new users to join automaticly and see the content and the conversation.

Describe the possible solution
Solution1: It would be great to have a second option beside "remove group and members" - like "remove group and keep members".
Solution2: It would be great to have the opportunity to decide weather the conversaion adds the group itself (keeping it up to date) or just the users once - (so you dont need to add 30 or even more users manually)
Solution3: Provide a checkbox in the conversation settings like: "update groups automatically..." or "do not sync members..."

I also tried solving the problem by creating circles for each calss but its not really convinient and rather confusion having a circle associated with an already existing group.

Since nextcloud is heavily used in edu context it would be great if you'd consider such a feature.
thanks a lot

The issue names no files, tests, or entry points. Start by tracing how Nextcloud Talk group conversations synchronize membership and how group removal is handled, then define the desired behavior with maintainers and cover the chosen workflow with tests.