OK found the workaround to fix the incorrect highlight menu on the docs (https://docusaurus.io/docs/api/themes/configuration#navbar-link - tl;dr

activeBaseRegex

supports multiple matches). Because the docs aren’t always arranged hierarchically according to the navigation, it was all over the shop. In any refactor we do (e.g. to diataxis) we can address it then. I didn’t want to do that now as it would change URLs and that’s disruptive for no really good reason. Changes going out shortly

Thanks super sleuth!