Katiesommons Please try playing in a clean user folder. Move the entire Sims 4 folder out of Documents > Electronic Arts and onto your desktop. When you launch the game, a clean folder will spawn with no content. (Your saves and other content will be intact in the folder you've moved but temporarily unread by the game.) Don't add anything to the new folder yet; just start a new save and have a look around.
If this doesn't help, check your antivirus for any recent actions involving Sims 4. For Windows Defender, this includes the Controlled Folder Access feature, which has been causing problems lately.