I wouldn't use CentOS for private/ desktop stuff personally.

Do you really need its features? Afaik, the "security" features you mentioned are mainly for server use. At least that's what I have in my mind right now when I researched possible candidates for my home server some time ago.

I think sticking with a "home use" distro would suit you better.

There are a few options as suggestions:

1. Stay on Kinoite

There's barely any configuration drift compared to the mutable Fedora. Therefore, it should be less buggy.

Fedora Atomic KDE gave me the best Plasma experience yet. I often tested KDE (I'm a Gnome guy myself, but here and there hop to KDE for a few months) and on most installs on other distros like Suse/ Workstation/ Debian, it got more and more buggy after a few weeks due to updates and tweaks.
So, bugfixes often didn't apply to my system, only the default one or the install from the devs.

I find Fedora's release schedule to be the perfect sweetspot between reliable, stable and up to date.

If you're really impatient, you can always switch to the nightly builds (on Atomic), which are more bug prone and rolling. Maybe, Plasma will be stable enough before it hits the official image. But you should keep at least one stable image in your bootloader.

2. Debian and Leap

Debian "just" got it's new release and will be stale for the next years. BUT, many of those Plasma 6 bug fixes will be backported to 5.27. Still, many of the QOL-changes are 6-exclusive.

OpenSuse Leap also gives you a great KDE experience and is pretty similar to Debian, both in release schedule and when the last big update hit.

3. Distrobox

You can use an Arch/ Tumbleweed container on Debian/ slow release distro to get all the newest KDE stuff on the outside and keep your stable base beneath.

Why? Because, in my experience, Plasma only gets more refined each update. As long as there aren't any new big features, there are about hundred bugs resolved weekly.

Or, you can do the opposite. Use something newer, like TW, Slowroll, Sid(uction) or Arch, to get the newest software under the hood, and use the Debian repo to get a stable DE.

Just what you prefer.

In your case, I'd settle with Fedora (mutable or Atomic, in your case the Kinoite version, as I'd prefer that one too), and just don't upgrade to the newest version.
The older version is always supported for a year or two, and you don't have to upgrade each release. The bug fixes always get backported if possible.