Answer by Jacket for Gnome Screenshot Copy Clipboard not working on Ubuntu 20.04

On my Ubuntu 22.04, the CtrlShift+Prt Scr shortcut does not work if the Screenshot program is closed. This seems to be a bug, which didn't happen on my last Ubuntu 22.04 machine.

My solution was to start the Screenshot program (gnome-screenshot) on startup, by adding this command as a startup application:

gnome-screenshot --interactive

I leave the application running in the background and I can now use the shortcut again, for quick and easy screenshots to clipboard.