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.
I kind of resent the whole "celebrity chef shows you how to cook" media thing because it makes something that should be approachable seen really intimidating for a beginner
Since I've begun "trying" in the kitchen, I eat way healthier than ever before, and most of my meals are better and cheaper than restaurant equivalents.