Akonadi QMYSQL backends that were created using <dev-db/mariadb-10.5.9-r3 may
be in need of a manual fix. Failure to do so could result in akonadi service
to stop fetching and sending mail for KMail or any other kind of issues in PIM
applications depending on akonadi like KOrganizer, KAddressBook etc.

Note:
  - All commands that follow are to be run by a regular user.
  - They will have to be repeated for any other user of KDE PIM.
  - Use your favorite terminal.

  1) Check if "mysql" system db is present:
     $ mysql -S /run/user/$(id -u)/akonadi/mysql.socket -e 'select schema_name \
         from information_schema.schemata where schema_name = "mysql"'

     The output obtained should look like this:
        +-------------+
        | schema_name |
        +-------------+
        | mysql       |
        +-------------+

     If so, then automatic DB upgrades will succeed, no further action necessary.

  2) If, however, the above query returned empty, add the missing database:
     $ mysql -S /run/user/$(id -u)/akonadi/mysql.socket -e 'create database mysql'

     Future MariaDB releases should upgrade without manual intervention now.

  3) Optional: You may have come here with an already defunct akonadi service.
     To manually fix the akonadi MariaDB backend:
     $ mysql_upgrade --defaults-file=~/.local/share/akonadi/mysql.conf \
         -S /run/user/$(id -u)/akonadi/mysql.socket

     Don't forget to restart the akonadi service afterwards:
     $ akonadictl restart

References:
  [1] https://bugs.gentoo.org/688746
  [2] https://bugs.kde.org/show_bug.cgi?id=409224