Kwin was a very good windows manager. It's very simple to configure, and administrate. It's just easy-to-do. But with the newest version (5.26.0-5.26.3) everything start breaking down, seriously. It's horrible, what they have done with kwin. 

Can't figure out why they people from the top accept all idea about destroy.

###1. Content is flickering
Many humans use multi-desktop to better manage with environment. You are just pressing a few key to switching desktop. It's very great idea, irreplaceable! But if you decide to fast switching between desktop, you will see a many artifacts. See attachment 1 [details]. i'm thinking an issue from OpenGL, or something else, like Vulkan.

###2. Broken copy 
If you press the wheel button on the mouse, you can duplicate advisable window to all desktop. With version 5.26.1 that possibility doesn't work anymore. See attachment 2 [details]

###3. Broken widget
I wrote that in a previous report. Many widgets always come back after restart. I'm using wallpaper engine for kde, maybe this, or something on KWIN side. I think a problem is located in configuration file. See my previous report: https://bugs.kde.org/show_bug.cgi?id=461144

###4. Totally broken version  
A newest version is not suitable for use. Seriously. Blank page, a lot of artifacts, glitches, crashing. Characteristic thing is a first screen have red solid outline.