Having no recorded issues running Trainz on Windows is news to me. I've run Trainz on both Windows and macOS (iMac is a type of Mac not an OS) and have had issues on both, sometimes the same issue, sometimes different issues :)
The Steam Deck runs SteamOS which is a Linux distribution developed by Valve. That uses the Proton compatibility layer to run Windows applications and games.
Solution, get a Mac! ;)
Sorry to hear about your pain John, good to hear that you don’t seem to have lost vital data. Not needed just before Christmas (or festival of your choice), but a frustration when it happens at anytime.
Merry Christmas anyway :)