Here are some pointers:
- the xfce session is started in qubes-session, here: qubes-gui-agent-linux/appvm-scripts/usrbin/qubes-session at main · QubesOS/qubes-gui-agent-linux · GitHub
- creating
~/.xinitrc
in sys-gui and setting XSESSION variable should be enough to switch to a different DE - if that doesn’t work, take a look at
~/.xsession-errors
in sys-gui
I don’t think anybody tried this before