@ReneHegewald I'll add a couple of points to what @Werner has already mentioned.
The board you are using RockPi 5B is not supported by Armbian. It is Community supported. That means Armbian doesn't have any resources that work on this board. All support for the board is done by community members like you. There generally is little that happens to community supported boards. Usually someone will submit some work to get the board initially setup and then shortly after disappear and nothing happens to the board again until it stops building at all and then it gets dropped. Unfortunately this is the reality of support for these boards. You are using software for free and it takes significant resources (both money and time) to make a board work well. There are very few people that are willing to donate a hundred hours of time to work on getting a board fully supported and maintain it over time with no compensation. Unfortunately the manufactures of these boards take advantage of the open source community. They in house initially do some minimum work to get something running, then once released move on to their next board and don't support the software and hope the open source community does it for free.
The best thing you can do, is build up your skills and contribute back to the community in exchange for the free software you are using.
q-bert got a reaction from lanefu in Odroid N2 - btrfs missing in mainline kernel