Frist and foremost you could replace the nfc antenna, power button and volume flex and wireless charging coil. But that will not slove a single issue with an iPhone in this condition.
Unfortunately you'll need to replace the entire back glass assembly (this part automatically contains a new wireless charging & nfc coil and often may of the other minor flex cable compents guled into the frame and backglass) , this is a difficult repair and takes about 3 to 4 hours. It requires excellent organization and attention to detail.
I only recommend using grade a or b oem pull parts from vendors like mobile sentrix beacuse a lot of the integrated flex cable compents often fail or never work in the frist place on after market back glass assemblies.
The process is very similar to the iPhone 12 pro max and iPhone 13 pro max., 15 pro max is the frist iPhone in the Promax lineup to offer iPhone 14 style replaceable modular back glass.
Be incredibly careful with the Bluetooth and 5g antenna that runs atop the battery compartment, this is the easiest part of the process to unintentionally damage compents and is directly soldered to the logic board making it inacessible to replace by most diy and chain repair shop technicians.
When I train new technicans on iPhone backglass assembly repairs I often suggest filming their entire process so they can go back and see where some of the confusing and oddly shaped compents came from and were place in the repair organization trays, bins or Mats.
Geting a screw or two scrambled in this process can be incredibly frustrating. And there is about 128 disassembly steps to fully remove everything that needs transfered from the frame.
I highly recommend replacing the back glass and potentially the charging port as well as the water and dust seal on this phone is beyond gone and glass dust from a broken back glass can wear down a lot of the numerous sensitive flex cables that snake through the device.
With the backglass in this state irreversible camera damage is also common
In my experience contuined use of a device in this condition will eventually brick it.
I'd offer to do this repair on a non profit (at cost) basis to crate a guide on it I've done this spefic repair about a dozen times in my professional experience repairing phones.
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