A KWin script that hides the borders of inactive windows.
git clone https://github.com/Jazqa/kwin-hide-inactive-borders.git
kpackagetool6 --type=KWin/Script -r hide-inactive-borders || true
kpackagetool6 --type=KWin/Script -i ./kwin-hide-inactive-borders
rm -rf ./kwin-hide-inactive-borders
kpackagetool6 --type=KWin/Script -r hide-inactive-borders