Hello
Finally the normal open source development process solved the problem.
With Mesa 25.3 all graphical artefacts and kernel messages disappeared.
The complete stack:
mesa: 25.3.3
linux: 6.17.11
libdrm: 2.4.125
qt: 6.10.1
wayland: 1.24.0
weston: 14.0.2
kind regards
Reinhard