gfxboot has never been used for UEFI, it is for BIOS (isolinux) boot only.
Replace keeps the EFI partition as is (does not format) because it should not remove other OS entries (Windows, other linux). I know of no solution yet for existing KaOS kernel images, only option I know is manually remove the kernel images in /boot for KaOS and keep all the rest.
This is not new though, has been the same for 2 years now, and seeing the amount of times reported, not a big issue so far.