As far as I can tell the default is XFCE. However, Linux is not MS
Windows meaning you can start off from a base system with just a
terminal. Then, you can install whatever graphical interface you want.
Keep in mind some desktop might be unavailable as disentagling them
from systemd/libsystemd et al is quite a difficult and complicated
task.

P.S.
For questions like these users are encouraged to use the forum:
dev1galaxy.org

--
If you can't explain it simply, you don't understand it well enough.
(Albert Einstein)
If you cannot make abstructions about details you do not understand
the concepts underlying them.