Hi
I have a similar question about this, I was about to test it for myself before I got a crash to dash, Im on xbox here, I like to set the destination airport in the world map to automatic, so in flight I get a active runway given to me.
I then go ahead and select the ILS runway in the mcdu.
As has been mentioned you then get the “Request IFR clearance” message pop up in the atc window.
I actually do all the atc myself, but I have no idea why I get this message when I have not really changed my flight plan, Im getting direct instructions from ATC and following them.
Have you ever tried not selecting it, do you still get guidance and clearance. as said I need to test myself but annoyingly I got a crash on last try.
Whats annoying is if i do request I get altitude change, such as climb to 10’000ft , then suddenly it wants me to descend back to 3000ft, apart from that all goes fine if I request IFR again, but be good if I dont need to request again.