It's the original Radeon HD 5770 1GB. Not powerful by today standards, but at 1280x1024 (old monitor), it runs Trainz Simulator 2 for Mac and Trainz A New Era at perfectly playable framerates. I would think TRS19 would be playable too, maybe just need to turn down a few settings. I'm considering purchasing an RX 580 with the flashed boot screen off ebay and then upgrade to Catalina using OpenCore. That's still less than 11.1 though. I just don't understand the requirements saying 10.12, but the app refuses to launch on 10.13.6.
Edit: I've heard you can run Big Sur 11.1 with some tweaks/hacks, but it honestly looks like more trouble than I'm willing to put up with and I've heard there are some issues anyway. Catalina looks much easier and doesn't seem to have any issues after installation. Also, having done a hackintosh before, I bought the Mac Pro 5,1 secondhand because I was "done" with the constant upkeep of a hackintosh install.