isabellronn Can you load a different household within this save? What about a new save? I'm not saying you can't play with your current household, only that this is a useful test.
Additionally, does the main house have any associated lot challenges, for example Off the Grid? If so, try entering the house in Build mode and removing the challenges.
If you can't play a new save either, 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 let me know whether it works.