I have performance issues with the new visuals and animations that are used in systemsettings.
Especially the rectangular icons with a blue outline that can be found for example in the latest "colors" settings.
The whole desktop becomes very sluggish during the fade in/out animations when I move my pointer over them.

I am not sure if it is specific to systemsettings or if it is a problem with a framework.
I have similar performance issues with Discover, but it is less severe.


STEPS TO REPRODUCE
- enable the show fps desktop effect
- open "colors" in the systemsettings and maximize the window
- move the cursor continuously over the different color themes to highlight them as fast as possible


EXPECTED RESULTS
- ideally ~60fps


ACTUAL RESULTS
- the frame rate drops under ~15fps


SYSTEMS INFO
- KDE Plasma: 5.16.0
- KDE Frameworks: 5.59.0
- Qt: 5.12.3
- Kernel: 4.18 and 5.1.8
- I am using Arch but I have also tested with a KDE Neon live USB stick.
- The system is an Intel i5 520M, it is old but it works very well with Plasma 5 and it shouldn't struggle that much (if at all) with fading animations on icons.
- I have no issue on a another machine with an Intel i5 2500 and an AMD gpu.


ADDITIONAL INFORMATION
- It seems that the drop in fps is worse when there are more of these visuals shown at the same time on the screen
- top reports that systemsettings is using ~20% cpu during the animation
- I have tried to set [Units] longDuration=0 in .config/plasmarc, the issue is the same
- I have tried to replace kwin with openbox, I can't measure the fps but it feels the same
- I have tried modesetting, SNA, UXA and Wayland. The issue is the same.