I'm long searching for a solution to do this is a much broader way.. On the OS level. Private Work A Work B Work C Ideally it would seem like a different user. (Filesystem, cmd-tab). But easily accessible like the three finger swipe. Fast user switching doesn't cut it. I even tried logging in on my local machine using VNC or remove desktop.. Is having 4 VMs the only way?
KDE Plasma has what they call "Activities". In its basic idea, it's kind of like fancy desktop workspaces. So, it does separate your windows into workspace-like groups, but you can also set what files and widgets are displayed on the desktop on a per-Activity basis.
So, you don't have a different filesystem, but you can have a folder or multiple folders displayed on each Activity's desktop. Also, shortcuts to different applications, including for example Firefox profiles, as well as different sets of widgets, for example I like to use the little post-it note widgets to write things down on.
And yeah, with that you can then just switch between Activities via a simple keyboard shortcut or by clicking an Activity-selector on your panel (if you've put one there).