Were you using a different install location than the default? I recommend adding the old installation location to the new version of the app, then clicking the "Scan for games" button. That should find all the existing games.
Regarding the game save data, we don't require games to handle saves in any specific way. A lot of the time a game will store its save data in the same folder where the game is installed, but sometimes a game may create its own directory in your user directory on your computer. Assuming you didn't explicitly delete anything, you should still have all your game data.