I have played a GalCiv III a fair bit (1300+ hours on Steam). Sometimes I play on my Windows box (Windows 10 Pro v1909), and sometimes I stream from the Windows box to my MBP (10.15.7). I've occasionally had a crash or disconnect of the streaming client, but I've been able to just reconnect and pick the game back up where I left off.
Recently I decided to try the 4.2 update. Since then, I have played for a few hours on my Windows box without issues, but when I try streaming from my Mac, it crashes the game. This is new behavior, as previously the Steam streaming client was not causing the game itself to crash. Even if the steam client crashed, the game would still be running, but now it is reliably crashing the game.