That warning is expected. Your layman has funtoo-kde-overlay properly installed.
I didn't add this to the layman repository list because I wanted people to be aware that this repository isn't meant to be used by anyone with layman access. This repository specifically bypasses the Q/A barrier that the Funtoo developers set up to gain beta access to KDE releases. This is potentially an unstable setup. The repository updates are automated and come with almost zero Q/A checks, so it's possible that it may break your setup at any time.
(Some Funtoo developers aren't super excited that this repository exists, so getting support for funtoo-kde-overlay here is going to be inconsistent at best.)