Vivianob Please test with your Mods folder removed. You can use "save as" so you don't overwrite your progress with the mods and custom content missing, but it's important to find out whether this error happens with no mods or cc.
If you get another error, let me know whether it's the same or different, and if it's a different code, please post a screenshot as you did here. And in that case, please share your saves too, if you're willing. Saves are in Documents > Electronic Arts > The Sims 4 > saves, and I'd like the affected one and its backups. You can tell them apart by their modified dates; the backups have the same internal number as the main save and a .verx extension on the end.
Please zip these files together, upload the .zip to a free filesharing site (Google Drive, Dropbox, etc.), and either post the link here or send it to me via PM. I would share it with another helper who deals with broken save files, and EA if it looks like a bug, but no one else.