Iphone 14 Pro Max charging issue with Macbook USB C port

A simple test would be starting up your MacBook in Safe Mode. Once started up, plug in Apple branded cable and then plug in iPhone. Does it charge?

You may get a popup wanting to know if the device should be trusted. Answer yes.

How does your title about iPhone having a charging issue relate to works via adapter in the socket? I really think you need to make an Apple Genius Bar appointment so the issue(s) can be observed and repeated to confirm an actual issue. I understand that you’re convinced the issue is entirely related to your iPhone. What happens if your iPhone works perfectly when they diagnose your iPhone and it works perfectly?

Genius Bar Reservation and Apple Support Options - Apple

Have you taken your devices to an Apple Retail Store or Authorized Service Provider?

You mentioned using an adapter? What kind of adapter? Can you post a photo of your charging cable and adapter?

Have you tried a different cable? I've not experienced a problem when connecting my iPhone 16 Pro Max to my 2024 MacBook Air. I'm not good at diagnosing problems with a MacBook, but you may want to post this in the appropriate MacBook forum and someone there may be able to provide you with more information on how to check the MacBook for problems.

Does the iPhone charge otherwise?

I understood your post. However, the MacBook identifies everything you connect to it. It could be possible there is something about that phone connection that could be diagnosed on the computer. As I said, I don't understand enough about the MacBook to diagnose anything, why I recommended the MacBook forum. Good luck.

Factory reset of which device?