I am trying to power the VIM4 from GPIO (applying 5VDC to GPIO 1 and 2) but it will not start. It is not drawing any power from the power supply and it does not start. It starts up when I connect power to the USB-C port. Is it not possible to power the VIM4 using the GPIO?
Nope the GPIO doesn’t support power input (with good reason),
You can supply input via the VIN port: