Was a nightmare making extensions in the previous version. The documentation was very scattered/cluttered between different jupyterlab versions. Don’t think I’ll be coming back to it for 4.0.
Additionally they often point you at their terrible discourse forum for asking questions. More often that not I don't see a good answer there either, when I merely search for one. I think their gitter channel has worked best for me so far, when they did not point me to that forum.
Typescript also helps a bit when compiling.
Sometimes I visit an old bookmark, that looked like part of official docs by the URL, but find it 404ing. Ultimately I agree, that good and accessible docs is not the project's strong side.
I guess I will have to figure some things out again soon when updating extensions to version 4.