White screen

Hi, and welcome to the Apple (user-to-user) Community.

Re: "Just one app is showing a white screen when opened. How to fix".

If you haven't already, you might want to try updating to the newest iOS version:

Eg: About iOS 16 Updates - Apple Support says iOS 16.5 is the latest.

or

If you have already updated to iOS 16.5, restarting your iPhone may help:

How to: Restart your iPhone - Apple Support

If you still need help:

Apple support has an article online that may help troubleshoot:

What to do: If an app on your iPhone or iPad stops responding, closes unexpectedly or won’t open – Apple Support

Else: If needed:

You might want to reach out to the iPhone Support: Team:

(There's a "Get Support" link at the bottom of their webpage... link below)

iPhone - Official Apple Support

All the best :-)