macOS Spaces (virtual desktop) allows the user to have multiple desktops PER MONITOR. When a user switches a space, it’s not the entire set of monitors, just the one they are in.
Is there a way to do this in Plasma 6, or… even GNOME?
You can have multiple workspaces per monitor on GNOME, just check your multitasking settings. I do this for my workflow since it’s more efficient for me.
In the upcoming Cosmic desktop by Pop!_OS, workspaces can be monitor specific, just like MacOS
I do this on Hyprland all the time, but it’s a tiling window manager. I’m not sure any desktop environments have support for it.
This is a very old feature request for KDE. It has not been implemented in almost 20 years so its probably very hard to do with kwin. Neal Gompa thinks this wayland protocol could make it possible in future, but with the current speed wayland protocols are accepted, this could take another 20 years.