I am having the same problem as the person here. I have root running on a Ubuntu terminal on my Windows machine and am working through the primer, and when attempting to plot graphs, nothing shows. I am able to save the plots and view them after running the code, but this is cumbersome. How do I allow popups to show.
When I run xterm as suggested in the linked question, I get
Xt error: Can't open display
DISPLAY is not set
ROOT Version: 6.28.04
Platform: Ubuntu 22.04
Compiler: gcc 11.3