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L7211/21/31 are tied together (CPU core) and correct voltage should be aprox 0.7V, after 10-15s (when board boots). It should drop from initial 1.1V aprox.

I don't know...

May have bad SSD, or CPU...

VDDA/P now? If missing, check diode mode to ground there. Probably need to replace U5200.

You should adjust R5215 untill get 0.9-1V at AUX_DET; with 5V input.

Do you mean 5V on both pins of R5215? That is only possible if R5216 is open.

What is the behavior of PPBUS_AON and 3V8_AON with charger alone?

What voltages do you get on CPU and GPU coils? Just in case, check AUX pins of J8500.

Increase R3555 value; test with 150-180K. Not sure what is U3540's VREF level, but 0.6V can be close to it. In such case, a slight drop on SENSE pin, can reset the Wifi module.

Dead NANDs...

You should have more components affected by corrosion; possibly broken traces too. Accumulated crap under BGA chips also may be a problem. Even a current, or voltage sensor can break the power on sequence. Liquid spilled repair can be a nightmare, without solution...

As per schematic, 787K & 158K. You should get close readings...

Pin 2 should be 3.3*100/(100+232)V; aprox 1V. High value resistors must be measured out of board.

CHGR_AUX_DET must be 0.9V aprox, with 5V input. It goes to aprox 3.5V when input switches to 20V. Replace R5216; it is open probably. Be sure R5215 has aprox 800Kohm. BTW, high value resistors must be checked out of board.

CP817 is 100pF capacitor and I'm sure it can't impede the board to boot. Just remove it. PPBUS_AON is the main (primary) power rail.

Check R5215/6 values (ohm scale).

No need of schematic, I already found it. Locate corroded components in boardview, then find corresponding values in schematic. "guide how to easily find all secondary level power rails in schematics" Almost all of them in pages 40-62. You have other on pages 116, 121 and 127.

Check diode mode to ground on all secondary power supplies (big coils).

"CHGR_AUX_DET is 0v" Fix that. What is CHGR_AUX_DET_SHORT_3V3 voltage?

Post U5200's basic voltages: P_IN, AUX_DET, SMC_RST_IN, VDDA/P, EN_MVR, AUX_OK, A/BMON. Remove F5200 and check C5252 voltage.