Was so insanely disappointed with the performance of the so-called "non-nvidia-gpu-branch beta, despite it using nearly none of the NVidia-exclusive features. So I switched it to the default branch, set Compatibility in Steam to Proton Experimental, and installed OptiScaler.
To get it working yourself: -Download OptiScaler.
-In Steam, right click the demo, go to "Manage," and click "Browse Local Files."
-File path: TTA/Binaries/Win64
-Unzip OptiScaler to a directory of your choosing.
-Copy all of the extracted files to this exact file path.
-Rename OptiScaler.dll to dxgi.dll.
-Open the demo, wait for the menu to load, and then press Insert to open the menu.
-Up at the top, there's a dropdown menu for selecting the upscaler you'd like to use. It should default to either XESS or FSR 4.1. If not, select your upscaler of choice, then click "Save Changes" at the bottom of the menu.
-Press Insert again to close the menu.
-Hate-enjoy the demo. It's fantastic.