I didn’t get any lag lag with my Kde. I only got Swag! 
Neither do i, i am amazed how fast is runs. Everyday i have the feeling that i did a clean install of the system. My eos install is already 1 year old and running butter smooth.
I am so happy with it and i cannot thank the community/maintainers enough 
.
I cannot say i did had the same experience with other operating systems in the past (Pop! OS (gnome), Zorin OS or Windows 11) over the last 5 years.
In my case the problem was not caused by system monitoring widgets, but by outdated Plasma widgets originally written for older KDE/Qt versions and not compatible with Plasma 6: (com.samirgaire10.Deepl-plasma6 and com.samirgaire10.chatgpt-plasma6). They did produce continuous QML runtime errors (missing functions like updateZoomTimer, PlasmaCore, etc.) and use QtWebEngine incorrectly, resulting in a binding loop, high CPU usage, and a continuous memory leak. Traced in journal.
Solution:
Remove the affected widgets from ~/.local/share/plasma/plasmoids/ and restart plasmashell. After removal, CPU usage and memory consumption return to normal.
How did you manage to zoom in on the widgets as the cause of the issue?
I just did see
.local/share/plasma/plasmoids/com.samirgaire10.chatgpt-plasma6/contents/ui/main.qml:114: ReferenceError: updateZoomTimer is not defined
in my sys log and assumed that this is related. I just double checked, had that and related ReferenceError entries also before the update to 6.6.
As far as I could see only
Apr 05 09:56:04 holodeck plasmashell[1964]: GBM is not supported with the current configuration. Fallback to Vulkan rendering in Chromium.
and finally some crashes
Apr 05 11:17:59 holodeck systemd[1701]: plasma-plasmashell.service: The kernel OOM killer killed some processes in this unit.
Apr 05 11:18:00 holodeck systemd[1701]: plasma-plasmashell.service: Main process exited, code=killed, status=9/KILL
Apr 05 11:18:00 holodeck systemd[1701]: plasma-plasmashell.service: Failed with result 'oom-kill'.
Apr 05 11:18:00 holodeck systemd[1701]: plasma-plasmashell.service: Consumed 1h 50min 14.614s CPU time over 1h 11min 38.803s wall clock time, 54.7G memory peak, 5.5G memory swap peak.
Apr 05 11:18:01 holodeck systemd[1701]: plasma-plasmashell.service: Scheduled restart job, restart counter is at 2.
were logged after the 6.6 update.
So obviously it is more related to some graphics issue then.
Though the deletion of the web widgets did stop the CPU usage and crashing.