5.5.68 is a minor security patch release. Any 10.x version has new features. If an app requires MariaDB 10.x, it presumably needs features not found in earlier major versions. It doesn’t matter if 5.5.68 is newer, if it’s missing features found only in 10.x.
On a personal note: I actually like Joomla and the way it’s admin panel is laid out. The problem is that if you ever need help with it you’re on your own. Answers to any issues are few and far between.