It's related to MDEV-7780 where @@version has become writable.

I don't know if it's technically possible, but if it is, it would be extremely useful to additionally print the real version (one returned by mysqld --version without an argument) in the error log upon startup and, better still, also upon a crash. We are going to have major problem with users setting this variable, because they will set it in the config file, will never update it in a timely manner (naturally, because they can get upgrades automatically), and we won't know which real version they report their problem against, finding it out will require additional negotiations and won't always be successful.