I tried again today with the 6.9.3 mainline and zen kernels, but with the same results. 6.3.32 LTS works just fine as does 6.8.9 zen.
I’m considering:
a) trying to bring this up with the Arch packagers
b) trying to build my own 6.9 kernel. I’m still reading about how Arch handles kernel builds.
Any advice for either of those would be quite welcome.