Noticed this with MariaDB.
When using lower than minimum DB version - server/proxy would not start, unless AllowUnsupportedDBVersions=1.
When using higher than maximum DB version - server/proxy will issue a warning, but will start, ignoring AllowUnsupportedDBVersions option.
Steps to reproduce:
Use fresh MariaDB 10.7 rolling release
Server/Proxy starts normally, just issuing the following warning in the log file:
Frontend systeminfo widget also has this warning:
Handling "too high" version should work exactly as "too low": do not start unless AllowUnsupportedDBVersions=1.