One thing you need to understand about iPhone batteries is that Apple has continued its anti-repair policies and has paired the battery to the logic board. That means when you replace the battery you will lose battery health information permanently, whether you use a genuine Apple battery or not. In addition you'll get a popup notification for a week or so that the battery may not be genuine, and afterwards there will be a permanent notification in your settings.
Normally you get around that by cutting the BMS, or Battery Management System, from the old battery and soldering/spot welding that BMS onto a new battery cell that doesn't have one. You could do that with a larger replacement battery, which would alleviate your issues of connector pinout and compatibility. You can buy battery cells that come without the BMS specifically for reusing the original BMS.
There are a couple of downsides to that approach, however. First, Apple has made another change to the battery health information in that they've encrypted it on newer models like the iPhone 12, so the normal programming tools like the Qian Li iCopy can no longer reset the cycle count and battery health percentage. There is a workaround, though; they make something called a tag-on flex cable that is inserted between the battery and the logic board and left in place permanently. Here's an example of what I'm referring to.
Iphone 12 Pro Max Battery Original Repair
The other downside is that the BMS will still have the maximum capacity information from the original battery, so the battery information may be inaccurate with regard to how much capacity the battery holds. Not exactly sure what effect that will have; I would assume the battery will work normally, but it's possible it may cut off charging when it reaches the maximum capacity of the original battery rather than that of the larger replacement battery. I'm not sure this kind of operation has ever been done, so we have no information on what will happen if you go ahead with it.
That would be my best suggestion as to how to approach this; I'd suggest that it would be worthwhile to get yourself a JC V1S or Qian Li iCopy programmer so you can reset the battery information.
Good luck; be sure to let us know how things go, as I'm sure I'm not the only one on this forum that will be interested in how your experiment turns out!
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