@QuaylinSims How much memory was used? Remember that the OS needs RAM, a lot of it, and if it's running low it will struggle to run anything else well. If Chrome then used a 1GB that's leaving barely anything for any other apps, let alone one as resource heavy as the game.
The workaround for you is to play in the new user account you created. I really believe, from the troubleshooting we have done, that the issue is your Mac struggling to run an intensive game and the main problem is memory.
With low spec. machines there is only so much you can keep adding to resource heavy apps like Sims 4 before it starts to buckle. This is why the Legacy Edition of the game was introduced, because the game is advancing, requiring more power and resources, and older tech. simply could not have kept up. Eventually that will happen to all our Macs