I use Kubuntu 24.10 and X11 (due to kontact not running in Wayland). My plasmashell is version 6.1.5. I read bug #388300 but this is focused on plasma 5. Maybe it is still the same bug? Here my details: I can add every widget to my plasma desktop. But when I add the Browser Widget to it, the whole plasmashell crashes and respawns automatically. The Browser Widget itself is not added to the desktop. I can add details if you want, but I hope you can just reproduce the bug.
*** This bug has been marked as a duplicate of bug 495758 ***