Game wanted to default to unsupported monitor resolution, meaning that trying to run in fullscreen resulted in "Cannot create Direct3DDevice" errors. I had to manually edit steamapps/common/Rise of Flight 2.0/data/startup.cfg to a resolution supported by my monitor.

Trying to use more recent versions of Proton than 3.16-9 resulted in a game that seemed to be fine, until I actually started flying, whereupon the framerate dropped to roughly 1 frame per minute. This I suspect is more due to my antique graphics hardware than a problem with Proton itself, as I see others have been able to use Proton 4.11 with no problems.

My graphics chip is ancient junk. Best results seen so far are about 9fps. I haven't yet tweaked the graphics settings, so I expect I can see at least some improvement on this, in time.