Can I connect the PG Pin to Vin directly ?
To better assist with the inquiry, can you please list the MPS part you are using?
Unless you need to know that the power is good you can leave it disconnected. This pin is information only not required for operation of the chip
The PG pin is an open drain of a FET, it is typically connected to VCC pin or some other voltage source with a resistor of slightly high value like 100kohms.
It is typically pulled low during normal operation, but pulled high if the output voltage exceeds 90% of the nominal voltage. Its also toggled if there is a thermal shutdown event or EN pin is pulled low.
The part datasheet will explain more on application specifics.
Correct, as noted by the schematic capture and also the part datasheet.
You can connect it to VCC or Vin pin.