Depends on the STEM. A whole lot of experimental science depends upon lab equipment that is either too expensive, too dangerous, or both to try and self-learn. Or it might be totally inaccessible no matter what. If you want to be an astronomer, you're gonna need time on one of the 4 meter scopes that is on top of a mountain that they don't just give public access to. Even if you had the billion dollars to build one in your backyard, the light pollution would make it useless. Wanna do medical research, you can't legally except under the supervision of somebody who already knows what they're doing and has access to a clinical population.

Programming and math are probably the two you can reliably self-teach, but probably the only two, and "programming" in at least some contexts might also benefit from extremely high performance or large capacity equipment you're not gonna find in a typical homelab or be able to afford renting from a public cloud.