Ubuntu – Alt+F2 not working properly

One Linux keyboard shortcut gives you quick access to all of your software and some useful commands. It’s like a portable command line, and it’s probably already built into your Linux distro of choice. Just hit “Alt” and “F2” at the same time to get started. Whether you want to force-quit a hanging application or quickly launch your favorite text editor, this shortcut is indispensable for Linux users.

Most long-time Linux users are probably already familiar with Linux keyboard shortcuts, but new Linux converts might not have discovered this simple shortcut yet. They should, because once you get used to using it you’ll wonder how you ever lived without it. It’s a great way to quickly launch your favorite applications, and can be used to do much more.

You need to type xkill in Enter a command prompt and hit Enter.

• Unity used to have this kind of interface when Alt+F2 was used:

  

  That was basically interface for entering a command with label Run a Command and Not a Dashboard(However it seems to be and that's what you are referring to.). It used to show suggestions as you type.

• But in GNOME interface is like this:

  

  And yes this doesn't show any sort of suggestions.

You can either create a Desktop Entry or define a keyboard shortcut in Settings → Devices → Keyboard to use xkill quickly.

I just had the same issue after migrating from 18.04 to 20.04, but I am using lightdm. Downgrading the nvidia-driver to 390 and restarting my machine solved the issue.

You can follow this link on how to update your drivers, but instead of the newest, choose an older one.

I only tried 390 so far, but a newer version might work as well.