Why is there no documented formula to convert to from this color space? A quick google and the best I could find is this Gist[0]. Searching for Oklab has a Wikipedia page[1].
It looks to me that all the "magic" is in the matrices used for conversion between Oklab and sRGB. The final conversion between Oklab and Oklch is trivial, and is documented in your linked Wikipedia article.
[0] https://gist.github.com/dkaraush/65d19d61396f5f3cd8ba7d1b4b3...
[1] https://en.wikipedia.org/wiki/Oklab_color_space