You will get the same version of Plasma and probably older versions of some other packages you use. With 5.27 being the last significant update until Plasma 6, you’re good on that for a while. Nothing will be newer than what you already have. None of your packages will get any updates beyond bug fixes and security updates, but it will be rock solid.
Kubuntu is also reliable and has newer packages. Personally, I don’t think there’s much to gain here unless you’re set on something that doesn’t have snap and don’t mind running older versions of most packages.