If needed, community categories can be L1 categories, which technically allows for subcategories under them. Having L1 categories is something the community discussed and approved here.
That’s something that is being tested as part of 🚧 Forum migration test instance (forum/fluxBB > community/Discourse) which is still under testing. Hopefully the migration will take place and messages can be merged to the same category here (moving messages around is technically possible).