Raspberry Pi 4 Model Rev 1.5 c03115 Just seeing the “rainbow-colored” screen of Raspberry. Tried with 192, 193, 194. Nothing happens. When flashing the normal Raspberry OS onto this microSD card it works.

Ok, I had to change the microHDMI-port. With RaspberryOS it worked on the right one (maybe on both? I did not check). But with ipfire I have to use the left microHDMI-port. Now I see… Thanks.