In my family it was jello, half of the half-set jello was mixed with whipped cream, other half cut into chunks, then mix in marshmallows, and fruit, and let it all set up.
I’ve never seen jello salad with cheese, veg, or nuts or anything, that’s wild, just cuz I’ve never seen it before.
17 isn’t that young, I was emancipated and thus a legal adult at the time (for convenience and work)… but yes I was fully aware of how the districts around me worked, because I used the choice program myself multiple times.
That didn’t stop me from warning the up-and-coming families, some years before it would have become an issue, so they could figure out what to do about it for themselves. None of my business beyond raising the warning call.