I was watching speed modeling video and saw haw cylinder flat cap was evenly rounded with a few edge loops very quickly.
https://www.youtube.com/watch?v=pX9pjtqanx4&list=PLTU7oKhL-me_h85qGNvavQwFigm7GX0xV&index=1&t=1s second 19. Slowdown play speed to 0.25 to see it clearly.
Apparently, the author did it with some key shortcut. I would like to learn with technique.