Some games, such as those that require another launcher, or multiplayer games in general, are less likely to work if they're outdated.

This is required to be done for any games not intended to be updated ever again, i.e. for old versions/downgrades, but not necessary for other games (i.e. to play games that received an update prior to going offline).

For each game to be skipped updates for permanently:

1. In your library, right click the game and select Properties...
   
2. In the Updates tab, find the Automatic Updates section
   
3. Make sure the selection is set to Only update this game when I launch it

Note: Games that fail integrity verification will be permanently stuck in the "update pending" state, so this method won't work.

This method uses Offline Mode to launch any game except for Family Shared games (and free trials/free weekend games, probably). No appmanifest editing or console usage required!

Why does it work? At some point, Valve decided to lift the restriction of playing outdated games in Offline Mode.

https://steamcommunity.com/sharedfiles/filedetails/?id=2926418252

1. Make sure you logged in with Remember my password ticked beforehand
   
2. Go to Steam > Settings, and under Account tab, ensure that Don't save account credentials on this computer is not selected
   
3. Exit Steam with Steam > Exit
   
4. Optional: Open the Steam > config > loginusers.vdf file in a text editor
   

   Default Steam paths:

   • Windows:
     
     C:\Program Files (x86)\Steam
   • Linux:
     
     ~/.local/share/Steam

   Under the desired user, set "SkipOfflineModeWarning" to "1"

Important: Never launch games you don't want updated outside of Offline Mode!

If you keep Steam open:

1. Switch to Offline Mode with Steam > Go Offline... > Enter Offline Mode
   
2. If the Play button reads Update, click on it and it will switch to Play. If it does not, exit the client and start it again
   
3. Launch the game
   
4. If you want/need Steam networking: Switch back with Steam > Go Online... and continue playing

If you only launch Steam when needed:

1. Edit the Steam shortcut/script from earlier
   
2. In target field/the launch command, append:
   
   -offlinemode
   Optionally, if you want Steam to truly be offline, add:
   
   -net_fake_state NoSteam
   If you want to make shortcuts/scripts for each game individually, also add:
   
   -applaunch <AppID>

Games that use Steam API may be launched directly via their executable and get detected by the client. It does not trigger an update from Steam!

Some games, including Source games, require additional arguments. In that case:

1. Launch Steam with:
   
   -console -dev
2. Launch the game once and close it
   
3. Under the Console tab, look for "Game process added/removed: AppID ### (...)"
   
4. In that line, find the game executable, and copy its file path and the launch options that follow.
   

   Example:

   Game process added : AppID 240 "'C:\path\to\game.exe' -game cstrike -steam", ProcID 26006, IP 0.0.0.0:0

5. Make a desktop shortcut/launch script for launching the game and paste the string from earlier in the Target field. Make sure to set the working directory (Start in) to the directory where the game executable is located!

Note: It may be necessary to create a steam_appid.txt file in the game's root directory if it does not already exist. All it should contain is the App ID. Otherwise, Steam API won't be present and the game may exit and attempt to have Steam relaunch it, which isn't the desired outcome.

If the game you want to play doesn't include Steam DRM or require Steam API, you don't need to use Steam to play the game at all.

This can be verified by launching the game using its executable while Steam isn't running. If it doesn't throw a Steam-related error, that's it!

However, in the same manner as the previous section; if the game needs additional launch arguments, you need to obtain them. Some games only require a launch option to verify if they're launched through Steam without any actual checks, so you can treat them the same.