After some more tries and checking the SD Cards twice, I tried using an older image of JetPack. Version 4.5.1 to be exact. This version installs correctly and after some minutes of install-duties it greeted me with a working LXDE desktop!

"So, what's next", I thought. "Surely it should be easy to connect one of my two Raspi-Cameras to the CSI-port and just have that displayed." 

Well, there is a short guide to do exactly that. Sadly, my camera seems not to be supported. At least not out-of-the-box.

Connecting it was relatively easy but when starting the capture command it just spat out a lot of command line information and then an error message telling me that there seems to be no camera.

I will have to see why that is, but for now it's off to bed.