@vman
Is the cmdline you use with vbutil_kernel contain nouveau.modeset=0? I can only think nouveau is being blocked either by the cmdline or else blacklisted in /etc/modprobe.d.
Hope you iron out the issues with your pinebook pro. Sounds like the GPU will make for a better experience than the poorly supported kepler based tegra. I doubt we'll ever see another Nvidia/tegra based chromebook.
@all
Linux 5.5+ kernels
There have been a series of regressions since 5.5 staring with an error with iommu and shared buffer handling.
I was able to get 5.5and 5.4 kernel running but with screen flicker and nouveau problems but 5.7 both with the stock debian bullsye and one compiled with my config fail to boot. I even tried the tegra_defcong but that will not load.
It Seems a new bug similar to the one that exists in 4.19 has emerged. The last 5.6 kernel I tried tries to load a non existent Nvidia firmware file. The tegra dev's do not test on tegra124-nyan so unless one of us sends bug reports or communicates we may have reached a dead end.
I shall be using the 5.4 kernel, which works, until my battery reaches EOL.