When launched, the game shows up as a tiny dot in the center of the screen. This dot changes brightness and color while the sounds of the intro videos and menu play. If I had to guess, I'd say it was launching at a resoluton of something like 2x2. This problem only happens in gaming mode. The game is able to launch from desktop mode, and seems to work fine there.

I still have my old 512 GB LCD Deck, and have confirmed that it still works on that one running the same version of SteamOS and Proton as my OLED, so the issue definitely has something to do with the OLED Steam Deck specifically. I also know that I'm not the only one who has encountered this problem. I've tried a number of different versions of Proton, and have tried doing resolution tweaks in the game configuration. Nothing has fixed it so far.