Endless loading screens have tons of causes. This isn't just one issue, it's a sign of something going wrong in your game.
Do you have any LastException files in Documents\Electronic Arts\The Sims 4 ?
- Delete the ones you have
- Trigger the error again
- Check if new ones are created
- If that is the case, please copy/paste the content here. You can open the file with any text editor.
Deleting the file won't fix your issue. Posting the info is meant for troubleshooting.
Also did you already go through this guide:
📓[GUIDE] Endless Loading | EA Forums - 5037259 ?