https://mariadb.com/kb/en/backup-lock/ has statement about BACKUP LOCK "This is mainly intended to be used by tools like mariabackup that need to ensure there are no DDLs on a table while the table files are opened. ", which isn't true since mariabackup, at least the open source version, actually doesn't use the lock.

I guess the doc should be fixed and provide a better example for BACKUP LOCK usage. I couldn't find any real life examples for the lock usage in the open source.