I'm on Debian Buster and an already seemingly functioning MariaDB 10.4.13 after upgrading from 10.3.22. However, the recommended mysql_upgrade script fails with the following error:
[..]
Phase 4/7: Running 'mysql_fix_privilege_tables'
ERROR 1071 (42000) at line 442: Specified key was too long; max key length is 1000 bytes
FATAL ERROR: Upgrade failed
Now, this question was asked twice on serverfault but sadly without suitable answers. After doing some more research this is probably due to the sum of my primary keys in some mysql core tables (no idea which ones since the error doesn't specify them) might be too long.
My DB seems to be working so far but I would like to debug the situation and don't know how I'd "attack it". I found someone in another mailing list who dropped all the mysql tables and re-imported them from another MariaDB installation but I'm afraid this might break the DB.