I have written a short guide on how to setup the Orange Pi 5 Pro for booting from the NVMe SSD. I know that the Ubuntu-Rockchip image already provides some scripts for setting up the Micro-SD card for booting from the NVMe SSD, but you need a way "larger" Micro-SD card because the image itself is that "large". The bootloader partition itself on the other hand is only a few MB in size. So technically you only need a flash device that is a few MB in size.
That's why I wrote this guide: https://gist.github.com/Mqxx/ce2077e97b7651781b0ccfceedff2423#file-setup-md