This is incredibly annoying as a photographer. I used to be able to work around it by pinching to zoom in a little bit, and then, without releasing my fingers, pinching to zoom back out and then releasing. Then I could see the top in the bottom of my image. This isn't working now.
I hate the automatic Zoom to fill. It imposes somebody else's aesthetic on the photograph that I took.
Rotating the iPad to horizontal does show the whole picture again, but now it's small. When I rotate it back to vertical, it fills the screen and crop the image and I can't see the full composition anymore.
My workaround, which I don't like, but it's all I seem to have now:
enter the stage manager view. In this view, the entire window is smaller, but it does show the whole 2:3 ratio photograph. It's ridiculous to have to go this route, because now the image is smaller.
This is one of the most annoying things Apple has done. Screwing with my photos is a no-no.