While I did not figure out a solution yet, but I found out some additional information and came to the conclusion that nixos must have built something weirdly. Thus I posted on the nixos forum and will likely only update there: discourse.nixos.org/t/…/36643
(Solved) how to deactivate hover click on kde plasma (and how did it get activated in the first place)? (feddit.de)
edit: I found the solution...