I started with basic on 8bit computers like Atari 800, TRS-80, Commodore 64, Apple II etc.... I learned by experimenting and typing in programs from various magazines and having to debug the typos out. I can't really imagine that would be a good way to learn in 2020 tho.
To the original question though about Flash. My gut tells me it's easier and more interesting to take more complete systems and modify. I'm thinking VBA meets Unity (I'm sure this exists, maybe Roblox?). The point is if I have a simple game and I just double click an object in that game and add 1-3 lines of code to change something, I feel like that would be a more approachable way to start than the start from nothing way.
There was a failed kickstarter trying to teach coding in a game (not the same thing as above but similar)
https://www.google.com/search?q=code+hero+kickstarter
The distinction I'm trying to make from Unity itself (and maybe this not an important distinction, not sure) is that it seems more intuitive to just double click the object you want to edit and get presented with a function to fill out the same way VBA did for forms. That is not how it works in Unity. In Unity you add script components which give you a blank script and I think requires a lot more knowledge what to put in that script where was if it was designed for learning maybe there would be more direction or more or simpler and easily discoverable places to add small snippets of code to change things.