My left side is coming along pretty nicely. The line is really nice. But the right side seems to drop a bit. And it isn't as "hard". And yet I can contract passively my right side better, which is odd. Also, when I contract the right side, theres a hole that forms on its lateral side just where the arm pit is.

Any idea to fix this?
Also, I'm on a strength routine but hopping on a hypertrophy routine in 2 weeks, so idk if it will changes something.

people rarely develop symmetrically

Or, perhaps you have an old soft tissue injury

Give it time mate

Hit db bench and see if there's a difference in the strength between your pecs, if you can do around a half rep or 3/4 rep more, I wouldn't worry about it. If you're able to get a full, clean rep off while your other pec is at 100% failure, I'd start working on that.

That hole you're describing in your right pec when flexing sounds normal lol.

Just keep training, focus on direct work later if needed (which will probably never).

Vouch