the u-boot from this thread works
https://forum.doozan.com/read.php?3,16017
followed as described and flashed the nand.
as a startingpint i used my own old gentoo image but it schould also work with the arch-linux image.
used an serial connection to change the the env var dtb_file to /boot/dts/ox820-stg212.dtb
and bevor i flashed the new nand i noted the old mac address so that ic an also set it back to the old.
its working great
https://forum.doozan.com/read.php?3,16017
followed as described and flashed the nand.
as a startingpint i used my own old gentoo image but it schould also work with the arch-linux image.
used an serial connection to change the the env var dtb_file to /boot/dts/ox820-stg212.dtb
and bevor i flashed the new nand i noted the old mac address so that ic an also set it back to the old.
its working great