@vw9ycxxz1bf4 Just because it's been mentioned as a source of lag, please disable the Discovery Quests. You'll need to restart after doing so, and the setting is on a per-save basis, so apply it to each save you test with. Your original post predates the patch that introduced this feature, but it's worth doing anyway given the other reports.
I wonder if some other background process is interfering. Please try playing in a clean boot:
https://support.microsoft.com/en-us/topic/how-to-perform-a-clean-boot-in-windows-da2f9573-6eec-00ad-2f8a-a97a1807f3dd
The one service to leave enabled is the EABackgroundService, which the EA App needs in order to run. Disable the rest as described.
When you reboot your computer, go through the Task Manager's background processes list shutting down any service that doesn't absolutely need to be running, for example anything from MSI Afterburner to RGB software might still be enabled. If you accidentally kill a critical process and it doesn't restart on its own, just reboot your computer again.
Don't open anything other than Sims 4 and the EA App while testing, not even a browser window. And please do keep testing offline.
When you test, start in one of the base game worlds and stay there long enough to see whether RAM use is increasing or stable. Then travel somewhere else and do the same. The idea here is to try to find a trigger for the memory spikes: a certain world or neighborhood, a build with certain lot traits, etc. You can let the game run while you do something else as long as you're around to check on it here and there.