10.9.2 introduced a new regression MDEV-30824. When a binlog generated from any engine versions is replayed on 10.9.2+ engines, depends on the character set settings, the replay could be immediately broken. This will break any functionalities relying on binlog such as replication.

Invalid line in binlog:

/*!\C utf8mb4 *//*!*/;

SET @@session.character_set_client=224,@@session.collation_connection=224,@@session.collation_server=33/*!*/;

Error:

ERROR 1115 (42000) at line 38: Unknown character set: '224'

This is later fixed with https://github.com/MariaDB/server/pull/2557 merged into 10.5, and is available in the upcoming minors 10.5.20, 10.6.12 etc. The fix prevents the previous releases from generating the invalid binlog that is not recognized by higher releases.

Merging this to latest minors does not address the issue when replicating from older minors to 10.9.2+. That means, any replication from 10.3, 10.4, <10.5.19 and <10.6.12 to 10.9.2, 10.10 and 10.11 will still be broken if non-default character set is used.

IMHO, we should also come up with another solution, that instead of fixing the binlog generation on previous majors, but to fix 10.9.2+, for backward compatibility.