In 2player if cappy jumps at the same time as mario jumping and holds in a 2d section you hover for a short time

it's a known glitch and used in runs...

Isn't that just a feature and not a glitch?

if you hold with 2nd player while in the air in 2D you hover, in general, it is indeed a feature and you don't have to jump with 1st player whatsoever to make that happend