Hey bollefjes,
We'd recommend reviewing this article as it provides steps to take to help resolve update issues with your iPhone: If your iPhone or iPad won't update - Apple Support
"Remove and download the update again
If you still can't install the latest version of iOS or iPadOS, try downloading the update again:
- Go to Settings > General > [Device name] Storage.
- Find the update in the list of apps.
- Tap the update, then tap Delete Update.
- Go to Settings > General > Software Update and download the latest update.
If you don't see the update in the list of apps or if the issue happens again, you need to update your device with your computer:
Learn how to use recovery mode if your computer doesn't recognize your device or your screen is stuck on the Apple logo for several minutes without a progress bar."
Thanks!