So the SYS rail provides VIN for for the EN IC (as far as I remember), which regulates 3V3PDR (the “ENXX” IC can be found below the realtek IC)
3V3PDR is connected to pin 6 of the M92 IC, if you measure 0V here after promting the console to boot, then something must be dragging down the 3V3PDR, I would measure the resistance to ground here.
Either that or the EN IC has failed or it’s not being told to turn on as a result of another fault.
So afaict the fault is most likely going to be an issue with the M92 or the soldering, the USB port or the BQ IC and maybe even the fuel gauge.
If the measurments above are good then I would start by removing the M92 IC and seeing if the console will boot battery only and if by removing the M92 IC 3V3PDR returns.
Alternatively, Hekate makes this process quite a bit simple and strips out a lot of this manual work.
I’m going to disregard this measurment as low end meters have trouble taking accurate in circuit readings here (even some flukes)