I had almost lost a save with 20 hours of progress because Proton thought the save synced over through Steam Cloud was corrupted. Proton made a backup of that "corrupted" save, thankfully, and I was able to manually restore that save. But that initial launch meant Steam Cloud synced over a fresh save instead of the save I had with 20 hours of progress. Be careful that this doesn't happen to you, and make sure you know where Proton puts your save data in case this happens to you.