The updating of the panels is very, very slow.
When I open or close an application, it takes 5-10 seconds before the taskbar icons are re-ordered. It is a delay in execution, in those 5-10 seconds I see the icons slowly, bit by bit moving to their position. An updated position about every second. Same for editing a panel. This is so slow it is unusable. I move the resize arrow with my mouse and the panel new border crawls to its new position in 5 to 10 seconds.

Everything else (start menu, start up, hovering over a task icon until it pops up, desktop effects, windows resizing, opening, closing, minimizing, system tray) is all responsive without noticeable delay or execution time.

Rendering is OpenGL 2.0, but OpenGL 3.0 makes no difference.

Debian 11 Bullseye
KDE Plasma Version: 5.20.5
KDE Frameworks Version 5.78.0
Qt version: 5.15.2
Kernel Version 5.10.0.-19.amd64
OS-type 64 bit

Processors: 4x Intel Core i5-6500T @ 2.50 GHZ
Memory: 16 GB
Graphics processor: Mesa Intel HD Graphics 530

I have Kubuntu and the "start menu" that shows the applications in the lower left corner is extremely slow when in search bar you write something eg. "medit" or "libreoffice".
I have not a high-end machine - i run multiple things, but when i execute a grep command in bash, it can find thousand of entries in some seconds, while the KDE menu may take 30 seconds or more to show a single entry written in search bar!!!

Note that i have de-activated "usb hibernation" -a lot of my devices are usb- using powertop. Also, i have moved tmp linux folder to other HDD - all HDD are plate ones, not SSDs - in order to limit events that may slow down my hdd.

if you need proof, i can take a video sample...

My system (using neofetch)

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