I guess I'm a little obsessed with having some sort of success so I kept going. I re-installed Flarum, and deleted the extension I was working on, even though that was overkill. But, I took an atomic bomb approach... Blew everything up, and started over.
yarn build this time because that's what you do in your video. Compilation was successful.
node_modules needed (for the production version that is). 🦄
So, just call me Mr. Dev Guru Ninja. I guess I'll be blasting out some incredible extensions soon thanks to all this learning... LOL, not really.