Are you getting a "Application / game is not responding. You may choose to wait for a short while for it to continue or force the application to quit entirely" message when trying to run a game or an application that takes a long time to start on GNOME 3.34 with Xorg, this causing GNOME Shell to become unresponsive / freeze with some screen flickering on top? This article presents a very simple workaround for this issue.