>All you need is an UKI on the EFI partition. UEFI has a perfectly sufficient bootloader already. I never found out what additional advantages `systemd-boot` would offer.
It gives you a UI to choose what to boot and edit the kernel bootline. You don't need it if your UEFI firmware makes it easy for you to do that, or if you have edk2-shell available, but those are not true of all systems.
Sure you get a boot menu. But the UEFI bootloader also shows a boot menu if requested. I think this feature is universal.
Editing the kernel command line on the other hand is something you never need except for debugging or recovery. For that you would have anyway an extra UKI installed, with a recovery system in the initrd.
But in normal operation you never ever even see the boot menu.
I still miss to see what vital advantages `systemd-boot` would offer. (And this has nothing to do with systemd as such. I use most of its modules. I just didn't find any compelling reason to use the boot module also. Some very simple hook script that triggers efibootmgr when needed is imho perfectly sufficient).
I've never seen a PC without a UEFI boot menu. That's why I've assumed that this is universal.
Who builds PCs without that feature?
Edit: I've had a look at the spec. Indeed a boot menu isn't mandatory (except when it is, for network boot options, see `PXE_BOOT_MENU`).
> UEFI specifies only the NVRAM variables used in selecting boot options. UEFI leaves the implementation of the menu system as value added implementation space.
But it seems to be common to implement this, as the spec also says:
> If the boot via Boot#### returns with a status of EFI_SUCCESS, platform firmware supports boot manager menu, and if firmware is configured to boot in an interactive mode, the boot manager will stop processing the BootOrder variable and present a boot manager menu to the user.
There are at least a dozen more references to a boot menu in the spec.
It gives you a UI to choose what to boot and edit the kernel bootline. You don't need it if your UEFI firmware makes it easy for you to do that, or if you have edk2-shell available, but those are not true of all systems.