How can you compare?
Magnitudes of more people use Windows and macOS than Linux* and they have yet to fail catastrophically.
* not counting servers and embedded
Parent post was updated to say "not counting servers and embedded", but dismissing smartphones -- literally the most popular type of personal computing device in the world -- this way seems to completely invalidate the point.
can know what -- that there isn't a backdoor? I can look at Linux source all day and not find the answer to that.
One dedicated person, can.