Hello again! I went the Stable route. After a clean installation of Debian Stable, everything displayed fine... in KDE.
But GTK applications had colored edges. After tweaking fontconfig and fontconfig-config with the same KDE settings GTK applications rendered nice fonts... except the smaller ones, who still display colored borders. Other applications like Telegram also display colored font borders in any font size... this is interesting because Telegram is a Qt program. In resume: I thought font rendering issues were something from the past but I was wrong. In 2023 it is still a serious issue affecting *every* Linux distribution. Anyway I will stay in Stable some time... My main applications are KDE based ones and a clean and crisp Konsole is a must for me. Thank you for all your tips.
