Someone calculated this, and concluded that satellites will remain visible for a few hours after sunset and before sunrise. In the summer, some of them would always be visible, in the winter there would be a few hours without a satellite ( see e.g. the Guardian article, https://www.theguardian.com/te...? ). Astronomers already automatically remove satellites from images, but that does lead to a loss of data. If there are this many satellites, it might well be that automatic removal of satellites makes it impossible to observe.

This is not completely true in an airplane: at least in my case, the volume that I listen to is set to have sufficient signal-to-noise ratio between the music and the airplane's noise. If I put earplugs in, the audio is blocked with some fraction, but the airplane's noise is equally blocked, hence I don't need a higher volume when I put earplugs in. The earplugs make the absolute volume just more bearable.

Singe dish telescopes generally fall into the second category of observatories that are affected by low-level RFI, and I'm pretty sure that holds for FAST. But even for e.g. the Murchison RA observatory that only has interferometers, they do test equipment beforehand, because they are a problem. ( I'm also a radio astronomer )

Radio emissions from the sun are not at all weak -- at most frequencies the Sun is the brightest source in the sky, stronger than CasA and CygA. You are right that daytime observing is possible with radio telescopes, but night time data is generally more valuable.

While turning a cellphone into airplane mode probably solves the problem for 90%, the digital electronics inside a cellphone that is turned on still cause some RFI. That's why for most radio quiet zones, electronic devices that need to enter the radio quiet zones are carefully tested / selected before bringing them on site.