@katinkamom Please test in a new admin Windows account. Make it local, as in, don't link it to your Microsoft account. You'll be able to launch Sims 4 without reinstalling anything, but your saves and other user data won't be available. That's fine for now and can be addressed later if necessary.
Test first with your antivirus active, and download MCCC or some other up-to-date mod to test with. If neither the Gallery nor your mod works, test again but with your antivirus completely disabled. As long as you don't do anything else at the same time, your computer should be safe, and you can reenable the antivirus as soon as you've loaded the game to have a look.
By the way, please make sure that your previous antivirus has been removed completely. Having two of them running at the same time is just asking for trouble.