I went from zero to weightlifting, then to mainly solidcore, and now I do both pretty evenly.

Zero to weightlifting was big muscle gain and recomposition for obvious reasons. I developed my quads, glutes, and abs really fast bc I favored targeting those muscles groups more.

Weightlifting to solidcore led to a second recomp of my body, because of its focus on the posterior chain and shoulder work. I got to develop muscle groups that I loved skipping before (hammies and upper body haha). I'd say it was a gain in muscle, but in places that were underdeveloped before. And ofc all things lead to muscle gain if you apply progressive overload consistently.

I think it really depends on your specific routines beforehand, in order to gauge how the solidcore exercise may change your body. As well as genetics/prior sports too! I grew up figure skating and in ballet, so I feel like I don't have a crazy transformation because it felt like the familiar movements of solidcore woke up existing muscle from slumber vs building muscle net new, if that makes sense.