"Superposable" means exactly identical in shape. Superposability is a thought-experiment to know 2 shapes are identical or not.
Our 2 hands are mirror-symmetrical, and of similar size; but no; they are not of identical shape.
Here is a small test. Stand facing the East. Bring your hands at front side of your body. Bring your palms together as shown in FIG2. Seems the shapes are same? (I'm ignoring tissue-details, just look the overall shape) Look closer. Think. Got anything?
For your left hand, now the palm-side is facing south. And its knuckle+nails side is facing north.
For your right hand, now the palm side is facing North. and knuckle+nail side is facing south.
They are so alike but they are so different!
If you now try to bring the both palm facing same direction, as in fig.3; your finger won't match. you may also change the orientation of wrist, and see any difference. No benifit, they wont "superpose". They are so similar but so different. They are sort of "opposite" shapes!
Yes our hands (left and right) are chiral and enantiomorphic from external morphology.
Image source: The Chemistry LibreTexts library. 25.7. Chirality in Organic Chemistry
Our 2 hands are not superposable i.e. not identical, because if you try to merge theme as follows the nails do not match.
The nails, knuckles, and darker, outer side of your left hand stay towords your left. And the nails, knuckles and the darker side of your right-hand, stay towords your right.
This particular example was taught in our college chemistry class.
Solomon & Fryhle's Organic Chemistry, 10th Edition, by T.W. Graham Solomons and Craig B. Fryhle, Wiley Student Edition.
Chapter 5 (stereochemistry)
Here is a google book result of an older-edition; Ed-8