Using Two Monitors in Ubuntu 20.04

Until two days ago, using two monitors in Ubuntu 20.04 was no problem. However, since yesterday, this is not possible anymore, even though I did not change the cable setup or anything. Also, when I go to "Settings"-->"Displays", it shows me "Unknown Display" whereas previously it had showed me the two connected monitors. I have an Nvidia GPU built in, any help would be appreciated.

Edit 1: Interesting, this problem does not occur under Windows where I can use my two monitors without any problems. My setup is a tower PC, an Nvidia GeForce GT 610 is built in.

Edit 2: The problem is solved now, cf. the accepted answer.

This kind of problems is typically related to driver issues. Check if, in grub, booting to an earlier kernel solves the problem.

Also, identify when was the last boot

$ journalctl --list-boots

and update (output may well be in excess of what is needed, but it doesn't hurt)

$ zgrep "linux" /var/log/dpkg.log* | grep " install "
$ zgrep "nvidia" /var/log/dpkg.log* | grep " install "

In addition to posting this output, please post the output of

$ inxi -v 2
$ xrandr
$ ubuntu-drivers devices

If you don't have inxi and/or ubuntu-drivers you can install them with sudo apt install inxi ubuntu-drivers.

If you don't have the latest nvidia drivers, I suggest you install them with, e.g.,

$ sudo apt install nvidia-driver-470

and reboot.

Two monitors with Ubuntu 20.04 LTS - now with the Linux driver nouveau

I have a somewhat similar system [as the original poster]. I updated and upgraded my Ubuntu 20.04 LTS in a Dell m4800 with nvidia graphics.

After reboot it can still feed two screens, one internal monitor and a 40 inch TV. I have them 'side by side' and can move windows from the internal monitor to the TV with the touchpad.

But I noticed that the system had automatically turned off the proprietary driver and was using nouveau (the free Linux driver). The performance playing video is good, I did not notice any significant difference in quality.

It works also for the original poster to switch to the free Linux driver, nouveau, and it can be a good alternative also for other users who are affected by this problem. (Let us hope that there will soon be a working solution with a proprietary nvidia driver too.)

To switch the drive, go to "Software & Updates", then under "Additional Drivers" and finally choose the Nouveau driver.