Boot:
At the time of this post/edit, I used this Letux kernel https://download.goldelico.com/letux-kernel/letux-6.4-rc2-lpae/
uEnv.txt on the SD card:
It works, I can point to a dtb, kernel etc.
Kernel command line: console=ttyO2,115200n8 root=PARTUUID=9f15472b-02 rw rootfstype=ext4 rootwait...