If there is no single being on earth that is able to eat it, I'd consider it non-edible. Even if all humans and animals worked together, they could at best eat some parts of the mountain. But that I'd rather consider eating rocks, not eating 'the mountain'.
If we define absorbtion of the mountain by a black hole as eating, I might accept that. Otherwise I double down. :P
Eating the entire thing is not generally a requirement for something being edible. You can't eat an entire cow, yet cow meat is considered edible (and if you want to say "but you can freeze a cow and eat it bit by bit", consider an adult blue whale - I don't think one human eats that much meat in a lifetime).
You can absolutely eat rocks, most of them aren't even that bad for you if they're somewhat smooth and not too large. Or just grind it down into a powder and bake it into bread, mix it into a milkshake or make a pill out of it. "healing earth" is a thing (helps with digestion) and it's just clay, you're supposed to either take it as a pill or mix it into water.