GRUB is still the standard bootloader in physical deployments because it is the most likely to work and supports most of the features you might want in a bootloader.
UKI based booting is interesting since it seems like it might support even more features. But the last time I tried to test it, there wasn’t a ton of documentation on it and the software still seemed a bit green and inflexible.
For example, my main computer right now has a completely redundant boot process. I have 2 disks which each have an efi system partition. And the root file system is btrfs raid1 across 4 disks. This was very easy to set up and completely supported by grub with no custom configuration needed. The only slightly tricky thing I had to do to install the second efi was to use an extra flag.
Primary issue I found with that software is there is no way to bypass certificate and old issues.