I've been using Notion a lot recently, and I was curious about what went into building something like this, and found this long list.
It's quite eye-opening to realize the complex web of dependencies involved in something like this, if you wanted to prototype something, I can't imagine having as a first step the requirement to first get all these things installed and configured etc.
Leads me to wonder if there are alternative stacks focussed on the non-scalable side of things (how to build the same thing with one or two people, if you don't have to care about serving a lot of traffic?)
(full list here)