DisplayPort not being picked up
Solution 1:
TL;DR Check if your DP cable firmly plugged in
As mine wasn't fully plugged in, so I had "no signal" message on my monitor. After I inserted the cable firmly I got the signal.
Before, I've tried to install mesa drivers and wake up DP manually with xrandr -d :0 --output DP-1 --auto
Eventually I removed all installed packages and it's working okay on blank Ubuntu 20.04.