Help my sims 4 won't even launch ;-;

Vandamm593  You can try loading your save in the new Sims 4 folder now, but don't bring over any other content at the same time.  If you can't load your main household, use Load Game to try a different household, play that for a bit, and try to switch back to your main sims again.  If that doesn't work either, move the sims to a different lot and try to load them and their lot separately.

At the very least, if you can get to Manage Worlds, you should be able to save your sims to the in-game library and place them, and any builds you want to preserve, in a new save.  But hopefully the save itself is salvageable through one of the above approaches.