System Activity is annoying. It's displayed "always on top" and you can't turn off this feature. Not really convenient. Also, you can't see other tabs that are shown by default in
Create custom shortcut like described in https://askubuntu.com/a/498816 answer.
For shortcut use "Ctrl + Esc" which will override default "Power Management -> Show System Activity" action.
Specify the action command:
pgrep '^ksysguard$' || ksysguard && pkill ksysguard