Comment 9 for bug 1982479

OK, I got further.

The distortion depends on the presence of the linux-modules-extra-5.15.0-*-generic package. I first did omit these extra modules and found a completely different behaviour without.

With linux-modules-extra-5.15.0-*-generic:

Kernels up to including 5.15.0-39-generic are fine. The bug came in with 5.15.0-40-generic

Without linux-modules-extra-5.15.0-*-generic:

System can't active ethernet and sddm hangs for unknown reasons when booting normally. But when booting into maintenance mode in grub, and just activating the "networking" (although it can't activate ethernet without the module), the system then comes up into a stable and normal X11 session, just the mouse pad not working (missing module) even with the 5.15.0-40-generic kernel!

So it must be
- something that came in with the -40 version
- probably something that is in the linux-modules-extra package and not the linux-image or the linux-modules package.