Is there any source that visualizes how SHA-2 works (including internals) with animated video or an interactive web page?
This shows an animation of the steps involved in computing a SHA2 hash.
I can't find a diagram of message expansion, but this shows a diagram of one round (SHA256 has 64 rounds):
you can check this repo, iti si creedt for Cryptography For Developers, Simon Johnson (pg. 218): https://github.com/in3rsha/sha256-animation
Check out CrypTool 2 (CT2). It is an open-source program offering an innovative visual programming GUI to experiment with cryptographic procedures and to animate their cascades.