Mouse stops working on main menu?

@psilocyberious  Please try playing with nothing else open other than Sims 4 and the EA App.  Before launching the game, open the Task Manager and close any other running apps, and also look through the background processes list for any services from apps like Steam or Discord that might still be active.  Especially problematic are apps that come with overlays, Discord included.  Please disable the EA App in-game overlay as well.

If that doesn't help, do the same as above, except this time, also try launching the game in windowed mode.  Go into Documents > Electronic Arts > The Sims 4, open Options.ini, search for fullscreen , and set it to 0 (zero).