Bonjour ebz8,
Bienvenue au forum!
Is it OK if I continue in English? When I read French I can mostly make a story of it, but when I write French, it is quite difficult for anyone to understand 
Yes! I would certainly do that!
I also had a problem with MariaDB when upgrading, and ended up with quite some repairs. It did get repaired though 
@Lapineige also has a hint in another thread: re-run migration 21. It might be that the workaround is specific for the problem at that time (something got broken and repaired upstream, I’d expect the same problem not to occur a year later)
I just re-read an earlier post, which mentions:
If you quickly and easily can take a snapshot, I would do that and first try re-running the migration ( with yunohost tools migrations run 0021_migrate_to_bullseye, I think ) ; if that does not work, and you can easily revert to your previous snapshot, try removing the yunohost-integration such as for Wordpress and Roundcube (I forgot why I needed to uninstall these two, out of all apps).
Good luck!