As an admin of a community, you can archive them at any time instead of deleting them completely.
This has the advantage that the community with its content remains for all users, but receives a visible indication that it is archived and the users thus recognize that they should no longer actively use it.
To archive a community go as admin to the settings of the community and set the option "Archive community".
Afterwards, the community can be filtered in the overview of communities by the filter "Archived".
Please note that by archiving a community it can still be used completely. If a community is no longer to be used, it must be deleted accordingly.