Power Management Help docs starts with text:
"This module is a configuration tool for managing Power Management in Plasma. It is a configurator for the PowerDevil daemon, that you can start or stop from the Background Services module in System Settings."
the part "... that you can start or stop from the Background Services module in System Settings." in the least is misleading, and at most incorrect. Powerdevil is a service started via xdg autostart for awhile now.
I suggest simply omitting that part of the text to avoid confusion.
See also downstream report,
for one case confusion caused.
Documentation mentionned is hosted at :