I tested Wayland + Sway (found an
experimental port on SVNWeb, fixed a couple of further bugs myself) on FreeBSD around a year ago on CURRENT, it works, at least worked, haven't tried ever since.
Currently only the GNOME3 port supports it, while, of the huge
kde5 meta package, only the screenlocker has been reported working properly, see
Graphics/Wayland on FreeBSD wiki.
Vulkan API is supported on Wayland too, amdgpu only as always
freebsd-ports-dank has several useful tips and fixes on Wayland usage