I also found the wip-kde-plasma branch in the Guix Git repository has some made some progress too. However, this branch has not been committed to in more than a year and only supports KDE 5.19.

This branch intentionally is on 5.19, as the Readme says:

Note 1: It might be worth making an older version of Plasma work, as this an
        older version has less dependencies. This is why this branch still
        sticks at 5.19.5.

And to my experience Plama is a beast and taming it might be much easier when using a less beasty version. This is why I recommend sticking with this old version for now and update only after this works.

-- 
Regards
Hartmut Goebel

| Hartmut Goebel          | h.goebel@crazy-compilers.com               |
| www.crazy-compilers.com | compilers which you thought are impossible |