I’ve found the source of the problem! It was the “amdgpu-pro” driver from AMD.
I’ve uninstalled it and the Plasma session now works again!
The bug is in the “libwayland-server.so” provided by the amdgpu-pro driver: it doesn’t have the symbol “wl_display_set_default_max_buffer_size”. I’ve found these evidences into logs when starting the crashing Plasma session:
dic 12 19:24:53 andrew-am kwin_wayland_wrapper[108837]: /usr/bin/kwin_wayland: symbol lookup error: /lib/x86_64-linux-gnu/libkwin.so.6: undefined symbol: wl_display_set_default_max_buffer_size
Then I’ve found this page: https://discuss.kde.org/t/fail-into-start-wayland-and-x11-not-show-title-bar-after-upgrading-from-24-04-to-24-10/24573
So I’ve uninstalled the amdgpu-pro driver, please pay attention since someone had some troubles after that. I’ve reinstalled the radeon driver from official repositories to avoid problems:
sudo apt-get install --reinstall xserver-xorg-video-radeon
but this may be superflous.
The missing symbol exists into the libwayland-server.so included into the default amdgpu drivers from Ubuntu/Neon:
$ dpkg -S libwayland-server.so
libwayland-server0:amd64: /usr/lib/x86_64-linux-gnu/libwayland-server.so.0.23.0
libwayland-server0:amd64: /usr/lib/x86_64-linux-gnu/libwayland-server.so.0
libwayland-dev:amd64: /usr/lib/x86_64-linux-gnu/libwayland-server.so
$ nm -D /usr/lib/x86_64-linux-gnu/libwayland-server.so.0.23.0 | grep wl_display_set_default_max_buffer_size
0000000000009c00 T wl_display_set_default_max_buffer_size
I hope this can help someone.
Bye