First of all… Thank you for this old thread. It allowed me to get Tumbleweed running on my brand new Rock 5B.
The UEFI software (an .img file) that amazingfate mentions above was easily flashed to a SD memory with the openSUSE Studio Imagewriter app.
I chose to download the DVD install media for Tumbleweed on aarch64 which is packaged as an .iso file and used the Imagewriter utility to flash the image to a USB memory.
(The above flashing was done on a Raspberry Pi 400 running Tumbleweed, if you wonder.)
The SD and the USB memories were then connected to the Rock 5B. The image on the SD card allows booting from the USB memory which then starts a normal openSUSE install. I chose to install a Gnome system to an internal NVME SSD.
The SD memory card allows the Rock 5B to boot from the NVME SSD too once the install is ready.