Blank display after startup and Idle time (Ubuntu 20.04)
Solution 1:
I've got also a blank display after the idle time kicks in. However, in my case this issue began as soon as I switched from the Ubuntu standard graphics driver (nouveau) to the proprietary NVidia driver (5xy). The video signal doesn't turn on again when using the mouse or keyboard. Thank you for the workaround of disconnecting and reconnecting the HDMI cable, this activates the video signal again.
GPU: GTX 1030
This solution seems to work so far for me (see link below): Disable C-State (try one parameter at the time to ensure you disable only what is needed) in the BIOS in CPU options which refers to idling the video signal (terminology and location varies depending on your BIOS version and manufacturer).
NVidia: Ubuntu 20.04 freeze on idle when connected to HDMI