Persistent white screen issues on iPhone 13 Pro after iOS 18.3.1 update

Reading the troubleshooting steps you already performed, it could be a hardware (battery? screen? other internal component?) failure but we, just users like you, cannot diagnose that kind of issue remotely, sorry.

I suggest that you contact Apple Support directly, using this link:--> Contact Apple for support and service , or make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> https://locate.apple.com/choose-country-region . After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.

You should contact the official Apple Support to get your device diagnosed, or visit an Authorised Apple Service Provider / Apple Store and let them check it.

Contact Apple for support and service - Apple Support

Apple - Find Locations

Has the battery ever been replaced? Did you check the Battery Health status?

And expanding battery can cause such issues.