Questions to ask of the midpoint
Ask whether the midpoint changes the protagonist's understanding, options, or cost. A good midpoint does not just deliver information. It alters what that information means for the rest of the story.
Ask whether the second half now demands a different emotional response from the protagonist. If the character is still engaging the story in exactly the same way, the midpoint may not be biting deeply enough.
Ask whether the chapters after the midpoint feel more dangerous, more compressed, and more irreversible. If they do not, the middle of the story may still be carrying first-half energy.