It’s not free, but you have to pay for it no matter what, so it kinda is, but cooking. Everyone should learn the basics of navigating a kitchen and the basic terminology.

Singing and dancing are both learnable free. Art in general tends to be cheaper. Usually anyway.

Intellectual skills are all fair game, there’s wide availability online. You need to start with Information Literacy though, to kinda unlock the rest. Otherwise you’ll waste too much time on bullshit.