Sims3 Game launcher doesn't work after deleting Userdata folder

Drensos2020​  If your game is working fine, I wouldn't worry about what's in the Userdata folder.

I would suggest not trying to manage competing Steam and EA App installs of Sims 3 unless you're good with details AND you don't mind doing some tinkering.  The distinct registry entries may break one copy or the other of the game, or the EA App may try to mess with your Steam install.  However, it's certainly possible that this would work, at least in theory.  So if you don't mind uninstalling and reinstalling again, there's no harm in experimenting.

The one other point to make is that if one install includes packs that the other does not, you'll need to keep two separate Sims 3 user folders (in Documents > Electronic Arts).  This is mainly because trying to play a save that has been exposed to an expansion pack without that EP present can easily break the save.  But certain other files in the user folder are sensitive to removed packs as well, although not necessarily to the same degree.  It's simple enough to rename one user folder and let the game generate another one; just make sure to always switch back and forth when you're switching between install types.