Created attachment 111429 [details] screenshot Currently Snap mount points are listed in settings window as you can see in my screenshot.
Confirmed. This also occurred to myself exactly the same way on Antergos Linux.
Systemmonitor just queries KSysguard which reads disk statistics from /proc/diskstats. There is currently no way to tell what "kind" of partition it is without consulting Solid or UDisks. This can surely be fixed but is non-trivial, re-assigning to ksysguard.
Created attachment 129356 [details] screenshot of settings window of Hard Disk Activity widget, Plasma 5.19 The settings window of the new Hard Disk Activity widget also lists Snap mount points in "Sensors details" section, under "Disk Throughput". Operating System: Arch Linux KDE Plasma Version: 5.19.0 KDE Frameworks Version: 5.71.0 Qt Version: 5.15.0
There is no sensor for snap mount points in Plasma 5.22.4. Operating System: Arch Linux KDE Plasma Version: 5.22.4 KDE Frameworks Version: 5.84.0 Qt Version: 5.15.2 Graphics Platform: Wayland