I hope you’ve recovered your data by now, but I’ll answer this in case anyone else reads it in the future.[br]
1.) Apple logo flash-screen goes dark. This is what a phone will do when it is auto-booting to DFU because it is missing information. This is never a screen issue. [br]
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2.) The iPhone 12 Pro is a split logic board (two halves soldered together like an oreo). Only the top board is needed for data recovery on some versions of iOS. You can rule out “bottom board problems” by splitting the top and bottom board using a special tool (this:) and then seeing if the top board will boot on its own. If not, then troubleshooting “why” is complex and beyond the scope of DIY repair. The only way to get data is to figure out why the phone won’t boot, and solve that problem so that it will natively boot and accept passcode. The ‘last ditch’ method would be to transfer the CPU, NAND and EEPROM to a known good receiver board with those chips drilled out.