> I wish there was a straightforward way to take the diff of all the Ubuntu variants.

It's not _exactly_ a diff, but here's a link to the Pop!_OS github page, which contains 149 repos (only 16 of which are forks) https://github.com/pop-os

> one could take Ubuntu and run a few shell scripts (I am grossly oversimplifying) and boom you are now running Pop.

That same link notes that the top languages for the Pop!_OS repos are Rust, C, Python, JavaScript, and (lastly) Shell. So not _exactly_ "a few shell scripts". (I don't know how accurate that really is, but I do know they've written a fair bit of Rust.)

(Note: I don't currently use Pop!_OS and think the name is absurd)