A massive release, containing improvements to dozens of components, widgets, and the desktop behavior in general.
Everyday utilities and tools, such as the Panels, Task Manager, Notifications and System Settings, have all been overhauled to make them more usable, efficient, and friendlier.
Meanwhile, developers are hard at work adapting Plasma and all its bits and pieces to Wayland. Once done, Plasma will not only be readier for the future, but will also work better with touchscreens and multiple screens with different refresh rates and DPIs. Plasma will also offer better support for hardware-accelerated graphics, be more secure, and enjoy many more advantages. Although still work in progress, 5.20 already offers users many of the benefits of Plasma on Wayland.
Check out the full announcement here: https://kde.org/announcements/plasma-5.20.0