Just wanted to add that I am also running into this issue, even without an external monitor connected.
I tried deleting settings and other suggested fixes but nothing was working.
Finally, I tried changing my computer's display resolution and opening Spine while using the lower resolution and that seems to have worked. I was then able to change the resolution back to normal and it seems to be working now.
It definitely seems like there is some issue with the graphics initialization on mac. For reference I'm using an MacBook Pro with an M2 Max with 38 core GPU and 32GB ram, running Sonoma 14.5.
