I have my KDE panel along the left side. I think the info here is still correct:
https://userbase.kde.org/Plasma/Panels
There's also a shot on that page of a vertical, left-side panel.
Added later: Well, I'm using KDE Plasma 5.18.5 in Kubuntu 20.04. If I right-click on the panel and click on "Edit Panel..." it puts me into the panel configuration mode or whatever it's called. From there I can move the panel to another screen edge by dragging the "Screen Edge" button with the mouse.