Exiting fullscreen reveals a black window with the game taking 1/4th of it in the top left corner.
Proton 3.16-9
Some audio stutter noticeable. Windowed mode does not work properly. Game itself works.
No issues
Slight audio stutter noticeable; Putting the game into windowed mode reveals a large black area outside of the game area (window is not properly resized to fit onto the game)
I had the slowdown that others reported happen infrequently; not enough to ruin the game for me. I tend to play this in quick burst, so it is extremely rare to happen to me. I didn't have the other problem of switching between fullscreen and windowed mode; it works perfectly.
Tried the Building Traffic mode. The game itself is perfectly playable. Performance slowly but surely gets worse over time, slowing down the game speed. Switching to windowed mode is not really possible as, when you turn off fullscreen, a giant black window with only a tiny fraction being the game appears.
Unfortunately I have to downgrade my previous rating due to the following issues:
Performance: continuous play, on "Madness" amount of planes, on the Zurich airport, after 280/300 planes: frames per seconds dropped significantly, and very sluggish input. I think it could lead up to crashes later on. I just shut the game down and restarted fresh.
Error: Maybe some kind of memory leak in Wine/Proton? The game isn't demanding graphically or computationally, I think. So there must be something else that's lowering performance over time.
The game starts fullscreen, if you then go to a window, you can't go back to proper fullscreen.