libmysqlclient >= 5.5.3, compatibilty with MariaDB
Upgrading to version 5.15 gives the following warning:
It is recommended, though not yet required, to upgrade your PHP MySQL driver (libmysqlclient) to >= 5.5.3 for utf8mb4 support. I am using MariaDB 10.3.16. This has support for utf8mb4.
Could it be that the check for the proper libmysqlclient does not include MariaDB versions?