I have a very strange Dell laptop with a UEFI firmware which does not support GUID partition tables (GPT). It does support running EFI binaries, and it will detect an ESP on an MBR-style disk (a partition with type id 0xEF).

When I attempt to install systemd-boot using bootctl, it complains that my /boot file system does not reside on a GPT partitoned disk.

systemd-boot works just fine on this system if I manually copy the binary to the ESP.

cp /usr/lib/systemd/boot/efi/systemd-bootx64.efi /boot/EFI/BOOT/BOOTX64.EFI