I’ve noticed that docs.kde.org looks very outdated. Lots of documentation is still referencing KDE 5 and brand assets still use old logos, etc.
Importantly, when you click help from within KDE applications, it takes you to the site that is still pointing to Plasma 5.
Based on KDE Documentation - KDE Community it seems that the only way to contribute to documentation is to directly contact the team. If I take myself as an example, I would consider submitting minor edits etc but not necessarily want to take it on as a job in general.