gypsyfolife Please try in a new admin Windows account. Make it local, as in, don't link it to your Microsoft account or any email address. You'll be able to launch Sims 4 without reinstalling anything, but your saves and other user data won't be available.
If this doesn't help, let me know what antivirus you use and whether it's listing any recent actions that involve Sims 4.
If it DOES help, we can try to fix your main account. Let me know whether the game is currently reading a folder inside OneDrive, as described here:
https://sims4.crinrict.com/eng/2018/07/how-to-find-your-user-folder/