We can't choose for you, unfortunately, only give you advice. My ~~advice~~ question is: Kubuntu and Debian (KDE Neon too, iirc) are an LTS distros, why would you chose them given your criteria?
For myself, I can recommend Bazzite or Aurora, if you are okay with using an immudable distro. They are both Fedora Atomic based, but Bazzite is gaming first, while Aurora is a general purpose distro.
openSUSE Tumbleweed is also amazing. It is rolling and generally one of the best KDE experiences you can get. It also has a snapper tool, which lets you to rollback to the state before the update or even further.
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