How do I secure stolen iPhone 16 Pro Max?

no, they can't enter it because of the passcode

and if they restore it to factory settings then the activation lock disable the from using it

Activation Lock for iPhone and iPad - Apple Support

so mostly they sell it to someone whos scammed and would not be able to use it

or send it to china for parts How Stolen iPhones Travel From Western Streets to Chinese Markets - MacRumors

As long as

• They don't know and can't guess your Apple ID password, and
• Any of your Apple devices that they have in their physical possession are locked with passcodes or passwords that they don't know and can't easily guess, and
• You don't fall for "phishing" attempts

they can't remove your phone from your Apple Account.

As for plants that reprocess stolen iPhones for parts, Apple added a little feature to iOS 18 that may start to put a crimp in their "business".

9to5Mac – Apple brings Activation Lock to iPhone parts with iOS 18

This may help --> Do's and Don'ts for lost iPhones - Switch… - Apple Community

Hello~ As you have correctly determined these are all phishing attempts to get you to respond. I am also pleased that you haven’t chosen to “meet” anyone anywhere to supposedly pick up your iPhone. I wish many others would conduct themselves as you have.

~Katana-San~