Thanks for checking it out - we found some issues with "start fullscreen" which were doing some strange stuff to some GPUs... new build is going up in ten minutes.
Did you do this? I have similarly bad perf on a steam deck with proton. I bound alt+enter to a grip button and was able to leave fullscreen but the performance seemed about the same.
new version has the ability to turn off the pixel-art upscaling filter [seemed to be the main culprit in tanking performances on some people's machines]
