…the Earth can support above sea level?
Everest.
My guesses.
I’ve heard science shows talking about past mountain ranges that have mostly disappeared. They seemed to infer that Everest was about the highest that they can get if they were formed by continental crust crashing into more continental crust.
It seems as though a volcano could grow higher but I’m not sure if the Hawaiian hotspot were located under continental crust it would be able to pour through it as effectively as it does through the oceanic crust. Maybe it’ll instead it would end up like Yellowstone.