Photo file size

Not necessarily related to photo file size, but storage used by photos is that the iPhone 11 and 11 Pro now capture multiple images with the different lenses allowing you to widen/narrow a photo at a later point (upto 30 days after shooting if I recall correctly). Much like Live photos/bursts, this information is shown as a single file, but will take up additional storage.

Another consideration

Both iPhone models are having 12 Megapixel cameras, see this page: iPhone - Compare Models - Apple

If you take the same kind of photo on both iPhones, the file size should be the same.

It will depend on the amount of structure in the particular scene, how large the image files will be.

When I look at the 12 Megapixel photos in the space saving HEIC format on my iPhone X the file size varies between 1.5 and 3.5 MB. The file size will be smaller if the photo does not have much detail in it. Then the compression will result in a smaller file.

The size of the photo is 4032 x 3024px.