I created a few Plan-G plans on the weekend which successfully loaded into MSFS 2020 after removing the square brackets from the exported file name.
I did find though that if I used Plan-G's Start Position button to assign a ramp / gate before exporting the PLN it wouldn't load into MSFS. If I left the default positioning for the departure airport and exported the PLN it loaded successfully and I was able to use the MSFS flight planner to assign a ramp position before loading into my flight.
I did find though that if I used Plan-G's Start Position button to assign a ramp / gate before exporting the PLN it wouldn't load into MSFS. If I left the default positioning for the departure airport and exported the PLN it loaded successfully and I was able to use the MSFS flight planner to assign a ramp position before loading into my flight.