I’m very sorry it felt sluggish for you but that’s likely down to your specific hardware configuration, drivers, GPU vendor + display server combo, etc.
I did not know that the most popular laptop CPU for many years, i5-7200U, with no GPU, is a rare combination of hardware, specific drivers, GPU (lol) vendor, display server (ThinkPad standard 766p LCD) is such a problematic configuration for KDE. You are just a KDE fanboy.
Also I installed Debian 12 Bookworm last July. It installs KDE Plasma 5.27 from the installer. KDE 6 never released until last winters, thereby making KDE itself ancient. Also, it was KDE 5.27, not 5.6. So my mistake there. KDE was far newer than I thought, still it could not support a mere common CPU laptop. I have no clue about their release nomenclature, because GNOME is easy, 40, 41, 42…