How can I integrate Navigraph into the glass cockpit of the King Air 350i in MSFS 2020, similar to how it’s used with the G1000 in the Cessna 172?
Thanks 
Jose
Hello! Welcome to our forum!
The default version of the King Air 350i in MSFS 2020 does not have any plugin support, so there is no official way to get any Navigraph integration working for this aircraft.
However, I am pretty sure that our G1000 Avionics Plugin would work if you installed this mod:
https://flightsim.to/file/61143/king-air-350-g1000-cockpit-mod
Give that a try, and let me know how it turns out!
Kind Regards,
Malte