Why is my iPhone screen time showing more than I used?

Here are quick check points for your comment answer:

1. Background Activity – Check if apps are running in the background.
2. Misattribution of Time – Ensure the screen wasn’t left on unintentionally.
3. Shared Device – Verify if someone else used your phone.
4. Incorrect Time Zone/Settings – Double-check your time zone and settings.
5. Apps in Foreground – Review active apps using Screen Time.
6. Sync Across Devices – Make sure other devices aren’t contributing.
7. Software Bug – Restart your phone and ensure iOS is up to date.

let’s reset the screen time data. First, turn off the screen time feature, then turn it back on. Check if everything’s working correctly now!

I was told by Apple Support that it was a known bug and that a fix would be released soon.

It probably just a bug, submit a report to apple