DebugPoint published a tutorial about installing KDE Plasma 5.22 in Kubuntu 21.04 Hirsute Hippo.
How to get KDE Plasma 5.22 in Kubuntu 21.04 Hirsute Hippo
The KDE team enabled the backports PPA which you can use to install and upgrade to KDE Plasma 5.22 in Kubuntu 21.04 Hirsute Hippo. KDE team released the KDE Plasma 5.22 recently with a fair amount of enhancements, bug fixes along with updated KDE Framework and applications versions.