Main difference with anki is that anki explicitly discourages trying to make dependencies between flashcards or decks. I tried to work out something like that into Anki, but as I saw it, dependencies were core to what I had in mind. There's some similar functionality in supermemo, but it's based on a tree, not a graph, so it was inherently limited.

No experience in mobile at all so that'll have to wait, but a GUI/website/app that works on most platforms is something I would like to work out eventually.

Mobile these days can be React Native which also "builds" for the web and desktop

Next.js makes React less painful

Solito makes Next.js + React Native a possibility today: https://news.ycombinator.com/item?id=30678100

I know it's possible. But the last time I did any frontend work, jQuery was the state of the art. So I decided that for now my efforts are better spent nailing the core experience and creating more courses.

I'm not saying you don't know it's possible, just providing you pointers on one possible stack should you decide to go down that path

My bad. I'll consider it when I decide to work on a GUI.