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Do you mean DFU restore? Completed without errors?

What is diode mode to ground reading at PPBUS_AON? Remove F5200 and check C5250 voltage. If no voltage, then post U5200's basic voltages: P_IN, AUX_DET, SMC_RST_IN, VDDA/P, EN_MVR, AUX_OK, A/BMON.

Check diode mode on any switch, like in pages 48, 76, 78. A good battery tester is a "must have" tool nowadays. https://www.cmizapper.com/products/battery-tool.html This is the cheapest and best option, especially designed for Apple repair. Harald has also a battery simulator for some MacBook...

You should diagnose the ports without battery connected; board alone on the desk. Check diode mode to ground on J3300; compare with good board, or reference table. https://www.masterliuonline.com/products/s-uem2-mac-usb-c-and-edp-meter Here is where S-UEM2 can help you a lot. It saves a lot of...

"PP3v3_s5 is 0.065 Diode to ground" Normal reading after U1900 was replaced? "PPVRTC_G3H is shorted" If pure short, start injecting with 1V.

I had one A2141 switching to 20V with shorted SSD (2V5_NAND), but I was not sure about M1 machines. Possibly problem with a secondary power supply. You should check all of them in diode mode; including master/slave rails.

You can test disabling a SSD power rail from working board.

You can't heat anything injecting voltage there. However, a good thermal camera can show you very small temperature differences. Injecting until 4V into 3V3_S5 shouldn't cause any damage. Remove CPU heatsink first.

Not true I think. You can compare with CS pin of any SPI chip; a BIOS from old boards, for example. It isn't steady 0V.

Keyboard information goes to trackpad board (on the way to CPU). So you need to have good working trackpad, to get also working keyboard. If JT400 has all power lines, you should test with known good trackpad board/flex. Just in case, inspect all circuitries from page 86.

Sudden death is many times caused by failed NANDs; even no short detected. If CPU can't access its dedicated partition on SSD, it can fully boot.

Did you test with battery connected?

https://openboarddata.org/?a=showboardsolutions&bpath=laptops/apple/820-01041

Dark column must be LCD issue.

I don't think, once you've replaced it. Possibly leaky cap.

Do you still have different behaviors on the USB-C ports?

Write down diode mode readings around actual U7800. Compare with new readings, once replaced the chip.

Check diode mode to ground on all secondary power rails. Pay atention to SSD power. Compare readings with good board, or reference table.

Did you look at USB redriver chip? That small one, which doesn't appear on boardview/schematic.

Should replace U7800.