You can completely replace the 1TB hard drive for your iPhone yourself, but you need to have enough technical expertise to do this. Besides, you need to prepare 1 main iPhone 14 Pro Max 1TB to be able to get the hard drive, I'm not sure it can be easily bought and the price may not be cheap.
I think you should sell your iPhone and buy a new iPhone 14 Pro Max with 1TB capacity, this ensures the durability of the device and avoids the risks in the process of replacing the hard drive.
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