This movie recently came up on Disney+ and I didn't see a thread for it. It is a pretty dull movie that might have been better as a series. It rushes past a lot of potential history and character development to pad out exposition with flashbacks. The best parts (aside from the camera guy following them around) are at the end - an amusing but terrible looking Pip the Troll, and the introduction of the Black Knight as a potential Avenger.
I mean, you don't have to like the movie, but Starfox and Thanos being siblings wasn't a "notion" made up specifically for the movie, that was something established in the Eternals comics in 1973. That's who the character is and always has been.