There are these existing bug reports:
- No way to promote/demote people in a group · Issue #5240 · vector-im/element-web · GitHub
- API support for changing a group member's privilege/admin level. · Issue #2855 · matrix-org/synapse · GitHub
Which will be covered by Matrix Spaces Milestone 4 · Issue #16206 · vector-im/element-web · GitHub
…but apparently there are no plans whatsoever for existing communities/groups to be upgraded or converted to spaces: https://github.com/vector-im/element-web/issues/15930#issuecomment-769093535