christer your account is on one of our older CentOS 7 servers which run MariaDB 10.6. As you've discovered, MariaDB 10.6 does not support the utf8mb4_0900_ai_ci collation.
Our newer AlmaLinux 9 servers run MySQL 8.4 which does support the collation you want.
If you would like to migrate to an AlmaLinux 9 server, first please read Migrating to another server and take all of the pre-migration steps required for your applications and databases. You should also read the post-migration section of that same document so that you'll be prepared for anything you might need to do after the migration.
After you've done so, please email support to let us know the date and time (with time zone) that you would like us to proceed with the migration.
