You said it hasn't worked for a while - did it work at some point?
You can try to set the resolution manually and see if that helps.
It was discussed last day in this forum. On Windows you add command line parameters to the exe to set the resolution, for example:
-screen-fullscreen 1 -screen-width 1920 -screen-height 1080
Not sure how to do it on a Mac but I think you can use command line parameters on Mac and Linux too but I'm not sure exactly how to do that since I'm not using those operating systems myself, but here one way is described: https://superuser.com/questions/466917/how-to-set-launch-options-for-programs-on...