Sigh... this evening, I finally got to test a newer KDE Live USB on Desktop 1 (which had issues with Kubuntu 25.10)
Salient part of the initial coredump - Looks like it's in libgallium *again*... (i.e. likely the same place as last time too), when doing a framebuffer blit in Kwin
Unfortunately, I am still getting crashes with this new version:
* Can now confirm it happens when trying to bring up any window
* Can also confirm that Kwin now pops up a very handy "Crash Handler" that can show the relevant coredump.
* The problem though, was that, after the first crash (from trying to open System Settings), the next dozen in quick succession (when trying to open the "Start" menu after waiting a few minutes) were happening so frequently, that I couldn't inspect if they were all crashing on the same thing.