This is an update for the HCL report from about a year ago. I reinstalled the workstation to Qubes 4.2, and this time it worked smoother than with 4.1 - no need to mess with the GPU to make the installer work, no visual artifacts, etc.
I still had to do the UEFI magic, though - after the installer reboots, BIOS did not recognize the boot option and goes directly to setup. I have very little idea how UEFI works (and no ambition to improve this knowledge), so I had to try a couple things. I don’t remember what exactly I did a year ago, but I think the instructions from the docs mostly worked, except that it seems to be for an older version and the files are a bit different (in particular, the file to copy to BOOTX64.efi is grubx64.efi and not xen.efi, IIRC).
I have only spent a couple hours on the reinstalled system, but everything seems to work like a charm - video, audio, network, … I haven’t seen any issues, and I think it may actually works better (e.g. the VMs seem to shutdown much faster, without the strange delays).
So far the UEFI issue was the only thing I had to deal with. Not a big deal, but would be good to have the instructions updated to match current version.