Im curious about that behavior as well, i personally assumes these were minor updates to the proton wine implementation of Valve, but i would like to know if this is really the case or not :P
Hello @oblitum, game updates are handled by the Steam client and this issue is already being tracked at https://github.com/ValveSoftware/steam-for-linux/issues/5644. Closing as a duplicate.
@kisak-valve I'm getting 0 bytes updates again lately.... I'm not using beta client (and I try to avoid them). I think this issue is back.
I have around 20 proton games in my library, and frequently when I restart the system or the steam client, there's updates for all of them, and in general I need to click update for each one, and all of the updates are zero download size.
This has been reported to happen with Steam at other times, but with Proton games it's simply for all games, all the time.