mariabackup keeps segfaulting under FreeBSD 12. I do not recall if it had problems last year under FreeBSD 11. However, it has had issues both with 10.3 and after upgrade to 10.4. My suspicion is that the problem lies in a dependency or some configuration with BSD ports or pkg. However, if it is a bug with Maria itself, I filed it here as well.
One hint I get is that it does not matter if I just pass it the --help command or try to run it with -u root &c: I still get the segfault both ways, so it seems to be something that happens very early on in the command.