Change to build ProjectM for LE11 Generic-legacy has been added https://github.com/LibreELEC/LibreELEC.tv/pull/7553 expect the addon to be available in the next day or so
The Generic x86_64 image switched to GBM/V4L2 graphics which means we use OpenGLES rendering not OpenGL required for ProjectM. The Generic-Legacy image still uses older X11 and OpenGL approach, and ProjectM should be available there, but then you lose HDR support. The Goom visualiser is OpenGLES compatible and similar to Project M.
Status Update: Drinking morning coffee and trying to work up some enthusiasm for Intel CPU hardware. I'm struggling..
Sadly not seeing any activity on github since February. Updating ProjectM to GBM/V4L2 must be a total PITA, I expect, and wondering if it will ever catch up to the latest versions of LE?