Hello! I tested debian-live-11.6.0-amd64-kde.iso and font rendering is just perfect, both in Konsole and the whole system.
I can't find a live testing kde iso, the only ones I found were based on cinnamon. I'm downloading a nightly build of kde neon, but download speed is awful, so no tests until tomorrow. The only bug somewhat related I found is this one https://bugs.kde.org/show_bug.cgi?id=463024 But I'm not sure if we are talking about the same issue. The main problem for me is I'm suffering eye strain because of all the rainbow colors around texts, and because this does not seem to be resolved anytime soon so I'm seriously thinking of migrating to stable or any other distribution with more up to date packages. I can't take this much longer. Greetings