I tried to install Ubuntu Server using the official Imager (so without downloading the image myself)
Ubuntu starts to boot, I see some command line output. Too fast to read it all, I see e.g. messages that the processor is not supported, then it looks like normal boot messages from a linux OS starting the default services. But after this, the screen is just turned off and went to standby, so it doesn't get a signal any more.
I tried different options in the
usercfg.txt, inspirated by other questions like this one
# Place "config.txt" changes (dtparam, dtoverlay, disable_overscan, etc.) in
# this file. Please refer to the README file for a description of the various
# configuration files on the boot partition.
This file didn't contain any settings. I also tried to just set
hdmi_safe=1 (uncommented). The only noticeable change is that I get a colored (like rainbow) screen on the start, without any console messages. A few seconds later, it shows the same behavior (screen turns off).
Why doesn't this work? Since I installed Ubuntu Server, I'd expect to get a console login on my screen after the boot.