Hey Henning,
cabal-install-solver was split out in 2021 and was first released with cabal-install 3.8, as you can see on its Hackage page [3].
The commit doing the split [1] and the corresponding PR don't have much discussion but the initial issue (2016!) has some [2].
I opened an issue to track the slip with the synopsis that you point out [4]. Contributions are welcome!
Thanks for your interest in cabal, and thanks everybody for the warming words!
Please, don't hesitate to submit issues on our GitHub if anything comes up.