[DELETE Thread; Issue Resolved]

I set my scaling back to 125%, and even with the new Native/Scaling option, it's still broken in fullscreen. You can't even toggle the new option if fullscreen is selected.

 

So, back to 100% until this is addressed.

 

I dunno why, but after three resets it finally stuck. *Shrugs*

[(The Jovian Concord: Update 25) Bug Report Megathread]

The resolution bug seems to appear at any resolution, not just 4K. Essentially, native resolution renders larger than the screen. I'm at 1080p, and the fullscreen cuts out 2/3rds of the display.