my iphone 14pro keeps turning off and on

Did you already check the Battery Health status?

Has it been dropped or in contact with water?

Restoring the iPhone back to factory settings without using the latest backup would be a way to rule out a software issue:

Restore your iPhone, iPad, or iPod to factory settings using a computer - Apple Support

1. Follow the Apple article to resolve the issue --> If your iPhone, iPad, or iPod touch won't turn on or is frozen ...
2. If not resolved; please follow the steps in the following link for support with this issue: If your iOS device restarts or displays the Apple logo or a spinning gear unexpectedly