In order to use an application's GUI within a SSH session, you need to login to the SSH session with the -X option. An example of this can be found below.
ssh -X username@th121-1
username@th121-1: ~$ code
With this example command, a user is logging into machine th121-1 with X11 forwarding. A call to VSCode is made within the SSH terminal, opening the VSCode GUI in the SSH session.