Stop Steam Sync Permanently

Solution 1:

Right click on the game in question, select "Properties". Go to the "Updates" tab, and uncheck the "Enable Steam Cloud synchronisation for {game name here}" checkbox.

For single game

Alternatively, to do it for all games, go to Syeam Preferences page, select the "Cloud" section, and uncheck "Enable Steam cloud synchronisation for applications which support it".

Interface for all games