iPhone 16 Pro Max battery not charging via cable under warranty

Greetings, I have an iPhone 16 Pro Max and it works fine, but sometimes when I connect it with the cable it doesn't charge the battery. I don't have Apple Care, I have the Apple company warranty which expires on October 17. I went to the Apple Store and they say it looks somewhat rusty. My question is if it's a part of the phone that was damaged because it's not covered by the warranty?

[Re-Titled by Moderator]