That's interesting, I always assumed projectM could never work on a RPI4, as it doesn't have the correct type of GPU to run projectM, since it is a very intensive GPU application
So in theory, ProjectM could run on a RPI4?
ProjectM is the one addon I miss most, since switching from a dedicated pc frontend (nvidia GPU) running Kodi to my RPI4
projectM is actually depending both on CPU and GPU, but differently for each preset.
It also practically runs on a Pi, with a decent speed. Main difference is that it needs to use OpenGL ES instead of GLX, which comes with a few limitations and generally lower performance. On my Pi4 it runs with full 60 FPS on most presets in 720p, and with decent 30 FPS in 1080p, so it's totally viable IMO.
Main problem for the add-on availability was the build system and some bugs, which didn't really support OpenGL ES as of the latest (3.12) release.
I've rewritten the build system, fixed many bugs and added a better API, so for the next projectM release (4.0) it should be possible to compile and run it on Pi-based LibreElec installations as well. Older Pi models might require a lower resolution, but should generally work as well.
I'll work closely with the Kodi add-on dev to make it possible. No ETA yet though as there are many other bugs - mainly rendering/Milkdrop compat issues - that need fixing. Hopefully in Q1 2022.