Make iPhone permanently trust computer?
[ this solution is assuming an Apple Computer ]

Make sure your Personal Hotspot is turned off. If your personal Hotspot is turned on every time your plug the device into the Macbook it will ask for permission and make you enter your PIN password.


  “When the personal hotspot is turned on, it will ask every time you
  connect your iPhone to a computer because it’s requesting access to
  the hotspot network over cable.”
  
  - Dan VanWinkle
  
  Source: https://www.igeeksblog.com/how-to-stop-trust-this-computer-message-on-iphone-ipad/