A series of loosely guided, non-interactive tutorials that require researching/figuring out on your own with some pointed hints when one gets stuck. Many of the online platforms are too hand-held and gloss over a lot of pretty important details about the how/why of writing, building, running a program. It'd be nice to see something that introduces a lot of correct vocabulary for unknown unknowns that equips someone with the tools needed to find answers on their own by knowing the right words to punch into a search engine.
Even just referring to the opening pages from K&R it says: "you have to be able to create the program text somewhere, compile it successfully, load it, run it, and find out where your output went. With these mechanical details mastered, everything else is comparatively easy." Jumping right into "hello world" that runs in a fully abstracted web IDE glosses over so much of the basics that a complete programming novice wouldn't understand.
My experience with being self-taught was that struggling with really basic things like installing the language/runtime/whatever and actually getting a hello world working to then write more involved apps was just as valuable as actually building a project because it required learning how to find answers and discover the correct vocabulary to articulate the language, system, tools I was using