All OSS has been ingested, and all the discussion in forum like this about it, and the personal blog posts and newsletters about it; and the bug tracking; and theh pull requests, and...
and training etc. is only going to get better and filtering out what is "best."
At best, what I find online are basic day 1 tutorials and proof on concept stuff. None of it could be used in production where we actually need to handle errors and possible failure situations.
There is barely anything that qualifies as documentation that they are willing to provide under NDA for lock-in reasons/laziness (ERPish sort of thing narrowly designed for the specific sector, and more or less in a duopoly).
The difficulty in developing solutions is 95% understanding business processes/requirements. I suspect this kind of thing becomes more common the further you get from a "software company” into specific industry niches.