Before the latest batch of updates, everything worked just fine without any performance spikes and without very high CPU & GPU usage.
However, ever since the 2020-07-19 update, the system sometimes almost freezes, with nothing responding to mouse clicks or any other kind of input (or only after several seconds delay).
Looking into htop, kwin_x11 is permanently between 20-40% CPU usage and even 5-20% GPU usage.
Now, to be honest, I did not check the usage percentages before the update, but I seriously doubt it could have been anywhere near that high given how perfectly the system performed even while running very demanding games (and browsing at the same time, etc.).
The usage percentages are permanently that high.
However, the performance is not permanently bad. It alternates between phases of completely normal usage and phases where everything grinds to a halt for a bunch of seconds (including the task bar).
Frankly, this could be anything from the last update. Some update to plasma, the Nvidia 440.100 update...
I'm at a loss at how to fix this, given how unspecific this problem is, but if I can't I really won't have a choice but ditch Manjaro for now
... or at least KDE, might try out xfce to see if the same happens.
Here's my inxi output: Dump your "inxi -Fxxxza --no-host" here and bookmark it
After running for some longer time, I checked htop again during one of these "slowdown periods" and kwin_x11 at that point consumes basically all of my 16GB RAM. After a while, it goes back to normal consumption.
I think at this point it is safe to say that there is a memory leak right now, which causes the slowdown periods and the current kwin version has serious issues. I'll switch to xfce for the time being, hopefully this will get fixed.