Actually, I haven’t tried there or Zandalar. I would also suspect that it is not available anywhere you can’t also fly the old way, such as Azuremyst/Bloodmyst, Eversong/Ghostlands, Argus, Timeless Isle, etc.
You can mount your dragonriding mounts like regular mounts in these places, but they can’t fly. Still usable though to some extent. Just hopped on one of mine on TI.
all I know is when I first mounted my new Griffin in Kul Tiras it was standard flying…then five minutes later I remounted and it was dynamic flying…so probably a bug.