Blue Square when planning wedding

Hi @WTLP555. This kind of UI error is typically caused by outdated mods. The most common mods causing this have been updated since they last "broke", so getting the current versions should help with your problem.

To check if it is a problem being caused by mods, exit Sims 4 and drag your Mods folder to your desktop. Then delete the file called localthumbcache from Document > Electronic Arts > The Sims 4. If you think you might accidentally forget to exit without saving after testing, copy your Saves folder to your desktop too, to back it up. Now open Sims 4 and see if you still have the problem. If you don't have the problem now, you can start the process of figuring out what from your Mods folder was causing it.