/backport to stable31

The occ db:convert-mysql-charset command changes the charset, not the ROW_FORMAT

It does both (if the table is in wrong charset):
https://github.com/nextcloud/server/blob/38768d1f8d8a0697c71580fa5821984bb10db7fe/lib/private/Repair/Collation.php#L62

if the table is in wrong charset

Which means it does not fix the problem from the warning.

And it is not its purpose according to the command description:
https://github.com/nextcloud/server/blob/38768d1f8d8a0697c71580fa5821984bb10db7fe/core/Command/Db/ConvertMysqlToMB4.php#L33

See also: nextcloud/server#34497 (comment)

yes sure - just wanted to point this out. As for most users their tables were created in a time where charset was wrong default and thus also their collation