Author here - happy to answer your questions...
Beware, there's a bug on ARM11-based Raspberry Pis (BCM2835 on Pi 1/Zero/Zero W and CM1) that crashes the VM when executing drawing functions. I'm currently investigating the problem.
I'll have to give this a try on my Raspberry Pi 4 4GB. I've setup Ubuntu, Arch, Kali, Raspbian, and Raspberry Pi OS on my Pis, but this'll certainly be the most exotic, given that it's not Linux. Do you know of any bare metal Forth- or Lisp-based systems for RPi?
There's the Interim OS project [1] (already discussed in another comment here) as a bare-metal Lisp and it might be interesting to port Movitz [2], a bare-metal Lisp project for x86 that seems to be abandoned for quite some time now.
There also seems to be a bare metal Forth implementation, pijFORTHos [3], but I haven't played around with that one so far.
[1] http://interim-os.com/ [2] https://en.wikipedia.org/wiki/Movitz [3] https://github.com/organix/pijFORTHos