Facts: It's large, fast, airplane shaped, painted white, and off radar. It stayed in the area, but ran away when fighter jets were nearby.
Since it's large, then it must be for holding things, so it's for transporting something. It's fast, so whatever it is transporting needs to get their quickly, or needs to run away from other things. It's distinctly airplane shaped, so it's optimized for flying through the air at cruising altitudes.
It's white, so it's not trying to hide at night or under cover. Commercial airliners are generally white, so maybe it is supposed to blend in at commercial airports.
It's off radar. Stealth airplanes are flat and small, this airplane is not. It does not have radar absorbing/deflecting abilities, it is off radar. Is it possible that civilian radar equipment is programmed to ignore certain transponders like photocopiers reject scanning dollar bills?
It knew the difference between commercial aircraft and fighter jets, and that the fighter jets were a threat. It didn't leave the area until it was in proximity to the fighter jets.
It could have been a test of the airplane's capabilities. But since it seemed to hang around the area for a bit, almost as if it was teasing pilots, I think it was testing the reaction time of the ATC and the fighter jets. The thought being, "If we need to get out of here, how long until they scramble fighters? And if they scramble them, can we get away?"
Could be that there are multiple factions in the government/military and one of these factions is planning for a quick getaway. That's the only way it would have "off radar" capabilities, civilians wouldn't be able to get a hold of that tech.
Is this Donald Trump and co's getaway van?