For my kid, I think volunteering and ECs were important for her fellowships. If you look at websites with bio’s of students who win these, they mention ECs and volunteer activities. These fellowships are not limited to STEM students so they take a broad look. The STEM oriented ones likely only care about STEM related activities/contests/awards.
Also, teaching experience came up in interviews with faculty who thought teaching was an important part of academia (a minority) but it did come up.
Also, regardless of fit hypsm is going still going to be more selective than say U Arkansas who e-mailed and offered funding after seeing gre scores in a database.