Plasma System Monitor hangs entire system

I’m using Fedora 35 KDE with closed source Nvidia driver for a very obsolete Nvidia card.

When I use Plasma System Monitor, the system often hangs (even ctrl-alt-F3 does nothing, only a hardware reset works). With the current software, I haven’t had any similar problems when NOT running Plasma System Monitor (KSysGuard works fine as a slightly uglier alternative).

When I was using the nouveau driver, I had lots of similar hangs, pretty much any time updates were occurring at the same time both in a visible window and in some other window hidden by that visible one. I don’t know whether there is any connection between those failures and the failure I’m asking about here.

I suspect the ancient Nvidia card is somehow relevant, because it is the only really unusual thing that could explain why I have this problem and most others don’t.

A google search found just a few other mentions of this problem, each of which implied it was much less common on systems where it happens at all than it is on my system. If I leave Plasma System Monitor running while doing ordinary activities, my system will hang within at most a few minutes. Often it hangs just starting Plasma System Monitor.

Is this a symptom of some more serious underlying problem with this computer? Or is it just a bug in that program that somehow isn’t hit by most users?

Are you using xorg x11 or wayland. If you are on wayland try with x11 and see if the problem there

I think I’m using x11, but I’m not sure how to tell. (I’m not an experienced Fedora user. most of my linux experience has been with a VERY stale version of Centos and even for that I’m not a competent administrator).

Process that are running include
and there is zero output from
ps -ef | grep -i wayland

Those are the best hints I have that it is x11 not wayland. Tell me what I should have checked instead.