@FlexRMeezy In case you're not sure, a clean boot is not the same as a clean reinstall of Windows. Clean booting means you disable all non-Microsoft services, temporarily, to see whether the game or app in question behaves normally. If it does, the problem is a conflict between that app and some other service. If not, you look elsewhere.
To clean boot, if you want:
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.
New EA and Steam accounts wouldn't help here—the problem is with the App itself, not your account data. I wouldn't have suggested installing the App through Steam beceause it introduces another point of failure. Instead, remove the App again with Revo and reinstall it from the EA website, running the installer as an admin (right-click the download and select "Run as administrator").
Or if you prefer, you can wipe your computer and reinstall Windows. That does solve most problems.