Comment # 9 on bug 1186896 from Takashi Iwai

OK, then it's likely some breakage in the recent upstream kernel.  At first,
make sure that the boot succeeds with nomodeset option for those new ones.  If
it works, the boot hang must be from amdgpu graphics.

You can find old kernel packages in my OBS repos, e.g. OBS
home:tiwai:kernel:5.4 contains the last 5.4.x TW kernel (equivalently),
home:tiwai:kernel:5.5 for 5.5.x, etc.  It'd be helpful if you can narrow down
which kernel starts showing the hang at boot by testing those kernels.