How do I fix iPhone 15 Pro rebooting repeatedly after iOS 18.4 update?

A normal user like me does not want to know what these analytics/diagnostic data mean.

These are meant for diagnosis when the iPhone goes for service or repair at the Apple Authorised Service Center.

Check for Conflicting Apps: If the issue started recently after installing a new app, try uninstalling it and see if the problem persists.

While I wouldn't personally act on the Analytics report you provided, I encourage you to explore it for potential improvements. Taking this step is unlikely to have negative consequences and may boost your confidence. --> General Troubleshooting iPhone Issues: St… - Apple Community

This may help you --> Share analytics, diagnostics, and usage information with Apple

If you are experiencing some serious issue in the function of the iPhone then...

Take your device to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support:

Apple Repair and Repair Status Check - Official Apple Support

Apple Authorized Service Provider

Find Locations - Location Selector - Apple

Contact Apple for support and service - Apple Support 

Alternatively, you may ...

Get a Genius Bar Reservation and Apple Support Options - Apple

Contact Genius Bar.

Manage Reservations - My Reservations - Apple

It's not always the iOS update's fault!  Many things can cause phone problems.  If you tell people you think it's an iOS update, it might make it harder to fix or find a solution for the real issue.

Remember, the right question often leads to the solution!

Was/Is your device Jailbroken? If that's the situation, please be informed that attributing the issues to iOS updates may not be accurate.

iOS updates aim to enhance user experience, boost security, and fix bugs rather than disrupt core features. The majority of the issues after updates might stem from underlying, unmentioned factors. Updates won't typically alter personal data but may refine settings or features. Backup before major updates for safety. Review Apple's update details and backup advice for a smooth process.

Kindly consider checking your settings and addressing any device issues before attributing the issue to external factors. This could be a pure coincidence that the iOS update affected the iPhone functions.

Before initiating a standard iOS update, it's advisable to create a backup. Have you completed this step? If yes, proceed with the restoration from the backup.

See what each update does: About iOS 18 Updates, About iOS 17 Updates, About iOS 16 Updates, About iOS 15 Updates, About iOS 14 Updates, About iOS 13 Updates, About iOS 12 Updates, and so on...