@aajc94 What antivirus do you use? (Even if the suggestion below helps, I'd still like to know because someone else is reporting the same issue.) It's possible your antivirus changed the permissions on the folder where you've installed Sims 4.
If you want a shortcut to troubleshooting, you can move the game elsewhere. First, set exceptions for Origin.exe and TS4_x64.exe within your antivirus, then create a folder elsewhere on your computer where you want the game to go. It can be almost wherever you want, but not within Documents or Program Files. Open your Origin game library, right-click on the Sims 4 icon, and select Move Game, then select the folder you've created. When Origin is done moving the game, repair it again.