I have “fat-chr” builder at GitHub that uses @krisnos’s script to support UTM’s native Apple Virtualization support (which requires EFI).
I replaced the script with @jaclaz’s version, but that did not work. UTM does not really report errors - so not sure what’s wrong - but it does NOT start using @jaclaz newer script. Switching back to @krisnos script, both 7.15.3 and 7.16rc4 work with EFI using the GH built images.
I’m pretty sure @jaclaz may right on the specs … but the “old” script has worked across few version with EFI - at least with Apple Virtualization (which is VERY picky). I cannot comment about proxmox etc, since you can use regular BIOS in proxmox (although I get @sindy is testing it)…