I'm so high on energy right now. / I'm so high in energy right now.
Everyone at the gym is in high energy. / Everyone at the gym is on high energy.
Which one is correct or are they both correct and natural usage?
In addition to rephrasing things, as suggested in the other answers, if you want to keep the word energy, I would use a different form and preposition:
I am so full of energy right now.
Everyone at the gym is full of energy.
Full of energy is a very common expression.
There is a fairly common locution "high in energy." That may have altered in some circles to "in high energy," but I have not heard such a usage.
"In high energy engines, heat dispersal is important" is perfectly acceptable, but that usage does not seem to fit your context.
"On high energy settings, Model A uses less power than Model B" is also acceptable, but again that usage does not seem to fit your context.
Because all three locutions are appropriate in some contexts, ngram will not help determine which is currently idiomatic in a specific context. Based on your examples, I think "high in energy" is what you are looking for.
I agree with the initial comments.
For the first one, instead of using
I'm so high on energy right now.
I think you'd be more likely to hear a native speaker say:
I'm so energetic right now.
For the second one, instead of using:
Everyone at the gym is in high energy.
you might be likely to hear this idiom:
Everyone at the gym is in high gear.
M-W defines high gear as:
high gear a state of intense or maximum activity — usually used with into or in : a project in high gear.
while Macmillan says:
high gear the state of performing extremely well or extremely quickly
The term high-gear isn't necessarily equivalent to "high-energy", but I think they are roughly the same when we are talking about people working out at the gym.