@Imogeeen Use Revo to remove Sims 3 again, then create a new admin Windows account and try installing the game there. Make the account local, as in, don't link it to your Microsoft account or any email address.
If that doesn't help, I'm wondering whether this is an overall Windows issue. The quickest way to address a broad swath of OS problems is with a repair install. This is the cleanest version of Windows you can get without wiping your data. Here's how (option two):
https://www.elevenforum.com/t/repair-install-windows-11-with-an-in-place-upgrade.418/#Two
This shouldn't delete anything, but if you get to step 14 and are NOT asked to keep personal files and apps, back out and start over.