I burned a copy of 20.04 onto an SD card and put it into my Pi4. When I powered up, instead of the expected rainbow screen, I got a message from my monitor that it didn't recognize the screen format the Pi was using. I powered down, then put the card into a Pi3B+ I have and got the exact same message. After tearing my hair out for a while, I finally took a close look at the config.txt startup file. I noticed that one of the last lines in the file read "hdmi-framebuffer=2" . I originally thought that this was saying that the Pi4 has 2 video connectors. Finally I realized that it wasn't saying "framebuffer(s)"; what it was saying was that the output is on the #2 connector. I moved the video cable to the 2nd connector and, voila`, up came the display, after which I proceeded to configure the system.
What i can't understand is why the system is directed to use connector 2 when connector 1 has been the default since the Pi4 was released, and why there is no mention of this anywhere in the release notes or other docs relating to 20.04.
