I don't think it's necessarily a show-stopper, but I'm setting it to a blocker now to make sure it's been looked at before the release. Please feel free to demote it after that.
If MariaDB-client (packaged by MariaDB) of 10.1-10.4 version is installed in the system, an attempt to install MariaDB-server 10.5 fails with a conflict error:
10.4 server installs alongside previous clients fine.
The workaround is to install MariaDB-client 10.5 together with MariaDB-server 10.5 (or before).