@jadeboonstrax The EA App budgets twice the necessary space for updates, so another 20 GB or so in this case. That should come out of the external drive's space, but if the internal drive is critically low on space, it's possible the App won't be able to cache data as it would normally do. So please make sure there's at least 10 GB free on C.
If that doesn't help, clear the App's cache:
https://help.ea.com/en-us/help/faq/clear-cache-to-fix-problems-with-your-games/
and repair the game: open your EA App game library, click Sims 4, and select Manage > Repair.
