Thanks for pointing to the Manual, I was not aware that this document changed.
I got it working now. One thing I added was the Airblast when picking up / putting away the tool by rewriting M24 and M25.
However, there is also the Airblast Button in the GUI. Is it actually connected to something?
Another point is that the ATC seems to forget the traverse Feedrate every time I start linuxcnc. When picking up a tool I get the error "Cannot do g1 with zero Feed rate" and have to go into the Rack Setup and click "Update rack parameters" (although the Feedrate is stated correctly here).
I now know that clicking "Ref Rack data" loads the Tools that are stored in the Rack. Unfortunately, It doesn't use the Tool Table "Rack" coloumn as I understood.
I assume this would require a Python script to read the tool table and make it usable via Gcode?
Thank you for your patience by the way, really appreciated!