I just found out about grid desktop view (ctrl + F8). Great this exists. 
I use 4 desktops with 1 row. I have 2 monitors.
First thing I noticed: It's hard for me to know what each desktop is and it's sibling in the other monitor.
I have to make a mental note that the 3rd square is linked to the 3rd square in the other monitor.
Second thing I noticed: The squares are a bit too small to be truly useful (when checking what applications are open in the desktop), since I have 4 squares per monitor. Turning desktops into 2 rows solves this but makes the grid view still confusing and I can't just move left/right to cycle through all the desktops since now I also have to take into account up/down.

Proposal: Make it work like it works in Windows 10. Full desktop on both monitors with a desktop switcher on top. I think it would make it less confusing. For instance when you open the grid it shows desktop 1 in both monitors, left and right and their open applications. You can drag an application to another desktop by dragging it to the desktop switcher on top, as well as moving applications from one monitor to the other of course.


KDE Plasma Version: 5.16.0