Baseline (Widescreen) Solution & Issues
Everything is Hor+ with the correct aspect ratio. Changing resolution while playing an emulated game makes the 3D background stretch to that aspect ratio until leaving that game (the emulated game adjusts correctly to the new aspect ratio).
Game Room defaults to the highest supported resolution. Only pre-determined resolutions can be used; manually changing the resolution in the registry to a resolution not listed in-game makes the game reset to a supported resolution.
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Eyefinity / Surround Specific Solution & Issues
4k UHD Specific Solution & Issues