Fresh boot, log into Cockpit as regular user, see Overview, Configuration,
"Performance profile: none". Mouse over "none" shows "Tuned is not running".
All correct so far.

Switch to administrative access, still it shows "Performance profile none" but
isn't grayed out anymore. Click on that gives an error

-->--
Change performance profile
Danger alert:Server has closed the connection.
-<--

which makes sense, as tuned is not running.

But after clicking the error away the performance profile ("virtual-guest" in
my installation) shows correctly and can be changed. Tuned is still disabled
but now running, Cockpit magically started it.

Changing the profile finally changes tuned to be enabled for system boot, again
magically and without telling the admin. This is confusing.

I suggest to change the error to something understandable, maybe along with
adding something meaningful to the docs.