The latest EDK2 (version 1.1 at the time of writing) supports FAT and ext4 file systems.
- The tumbleweed package dtb-rockchip-6.15.6-1.1.aarch64 puts…
- rk3588-rock-5b.dtb (and quite a lot of other dtbs) in the…
- /boot/dtb-6.15.6-1/rockchip/ catalogue and adds a symlink at…
- /boot/dtb (which is located in the systemroot partition).
EDK2 looks (as default) for dtb and overlays in…
- /dtb and…
- /dtb/rockchip
The computer has a separate EFI (FAT) boot partition mounted at …
- /boot/efi
Right now the systemroot partition on my computer is btrfs and that might be the problem as EDK2 does not support btrfs, only FAT and ext4.
So I’ve tried adding a new catalogue to the (FAT) partition mounted at…
- /boot/efi called…
- /boot/efi/dtb and placed a copy of…
- rk3588-rock-5b.dtb in that catalogue.
…but the system hangs during boot. 
…even after adjusting the path to the dtb in the EDK2 settings.
Any suggestions?