You’re barking up the wrong tree and fucking up your life by doing this.

Split the streaming/gaming duty to a different device that can be operated in the way the user expects.

Wherever you disconnect shutdown signals from will be relied upon by something down the road and you’ll end up with a weird messed up broken update when that happens.

Uh keep in mind they could just unplug the computer. Software limits are good, but if they really want to shut it off, they'll find a way.

You'd probably want to look into dbus or PAM.

Or google, how people fixed that they were not able to shutdown from GUI. That's a more common occurence than limiting it.

I don't know if Fedora (or plasma) do things differently but the normal default is that you need sudo to reboot/shutdown/etc.

Then on basically all distros using systemd this behavior is modified via logind session and polkit. So the first thing to look at would be if a shutdown rule exists in /etc/polkit-1/rules.d/ that allow users in a certain group to shutdown/reboot in the first place.

Mine looks like this:

/etc/polkit-1/rules.d/50-shutdown.rules
polkit.addRule(function(action, subject) {
if ((action.id == "shutdown" ||
action.id == "reboot") &&
subject.isInGroup("wheel"))
{
return polkit.Result.YES;
}
});

So every user in the wheel group can do it without password prompt. Without this UI elements for shutdown/reboot will try assuming they have the right but simply fail.

systemd-inhibit seems like the right place to look, ~~but I have a vague feeling that gnome can override it.~~

https://www.freedesktop.org/software/systemd/man/latest/systemd-inhibit.html

Maybe with some tweaking itll be unoveridable except for root?