Does anyone know how the development of the GPT is?
I believe it is still on the ToDo list, but nobody has done more than look at what might need to be done. Not enough people, who know what they are doing, to do it, and more important things need to be done first.
If you add a GPT disk into airboot, it adds MBR record making GPT unusable.
The later versions of the LVM engine (in ArcaOS 5.0.4, I believe) will refuse to touch a GPT disk, to prevent problems. That can be overridden, IF you know how. Don't do it, unless you are prepared to lose all of the disk contents. If you still have the older LVM engine, DON'T MESS WITH GPT DISKS.
Maybe AirBoot can be extended independently to continue booting from a GPT boot partition on a secondary disk without modifying that disk.
It appears, to me, that Air Boot needs to be replaced to support UEFI without CSM support, so it may be possible to do something with it then. Air Boot, as it exists today, barely fits in the space allowed, so expanding it is probably not an option.
Perhaps a different tool like Acronis TrueImage
Acronis TrueImage is the ONLY windows backup tool, that I know of, that will do backups, and restore to a different disk setup, successfully (it is the ONLY windows backup, that I know of, that actually works as it should). If you have a Seagate, Maxtor, or Samsung disk (even in an external USB drive), you can use the Seagate DiscWizard (search for it). That is a free, limited, version of Acronis. I have used it a few times , while testing ArcaOS installs. While testing, I did install win 10 onto a GPT disk, did a backup, wiped the disk, and restored to it, changing it to be an MBR disk. It worked. YMMV.