Is the Classic Shell part of the Windows 10 system, or do you have to download it from the internet?
It’s an add-on you download from the internet.
I don’t use it but your question got me curious.
Here’s a link that discusses different ways to make W10 look and feel like W7:
https://www.howtogeek.com/277448/how-to-make-windows-10-look-and-act-more-like-windows-7/