For example, https://userbase.kde.org/KSysGuard save its setting on /home/user/.config/ksysguardrc.
Where https://wiki.gnome.org/Apps/SystemMonitor save its settings?
There are no settings files on .config or .gnome.
I opened fatrace and ran gnome-system-monitor, but it did not seem to read any settings file:
panel-1-whisker(4901): RO /usr/bin/gnome-system-monitor
panel-1-whisker(4901): R /usr/bin/gnome-system-monitor
gnome-system-mo(4901): O /usr/share/gnome-system-monitor/gsm.gresource
gnome-system-mo(4901): RCO /usr/share/applications/gnome-system-monitor.desktop
gnome-system-mo(4901): RCO /usr/share/applications/gnome-system-monitor-kde.desktop