Here's a KDE Plasma 6 power feature you probably had no idea existed.
Hit Meta+T on your keyboard.
You can define tiles on each of your screens.
Now grab a window and hold shift - it will snap to the closest tile!
This way you can arrange windows on your screen(s) in a way that will keep them sharing your screen's area without ever overlapping.
Doing this manually always took so much time and was so fiddly...
You're welcome!