The process is explained here: https://mariadb.com/kb/en/partial-backup-and-restore-with-mariabackup/
This process is way too complicated. In a situation where there is a multi-tenant database instance, recovering one database / tenant is a way too complex process.
MariaDB really should do more of the work here. That the process is different for partitioned and unpartitioned tables is one such issue, but the whole thing is manual and error-prone.