Customize KDE Plasma to my favor

Install Sweet Theme
System Settings -> Appearance -> Global Themes -> Get New Global Themes
Sort by Rating and install „Sweet KDE“

Set Plasma Style to „Sweet“

Set Colors to „Sweet“
And change to blue highlight Colors

Set Window Decorations to „Sweet-Dark“
Also there set Window border size to „No Borders“
Also there tab „Titlebar Buttons“ remove the „pin to icon“ (drag it out of the title bar to the below area containing all the other icons)
Also there choose the edit button on the „Sweet-Dark“ thumbnail and change the button size to „huge“.

Check in System Settings -> Display and Monitor -> Compositor if it is turned on.
If not check „Enable on startup“.

System Settings -> Workspace Behavior -> Desktop Effects
Check Background Contrast
Check Blur
Check Dim Inactive
Check Slide Back
If you do not find Magic Lamp or Translucency etc. check the filter settings not to exclude unsupported effects.
Can be they won’t work goog with nvidia dkms 470

Open e.g. Dolphin file manager
Click on the System Menu in the above left corner of the window.
There choose „special window behaviour“.
Set Windows class to unimportant
Delete property with window name containing the dolphin string
Name the rule Window setting for all windows
Add Active opacity rule -> Force -> 100%
Add Inactive opacity rule -> Force -> 80%

System Settings -> Window Management -> KWin Script -> Get New Scripts.
Search for „Force Blur“.
Install version 0.6.x.
Open console, paste and execute

mkdir -p ~/.local/share/kservices5/
cp ~/.local/share/kwin/scripts/forceblur/metadata.desktop ~/.local/share/kservices5/forceblur.desktop

In KWin Scripts settings enable Force Blur -> do some settings -> and Apply (maybe disable Force Blur and enable it again – then apply).

Install lightly shaders
Navigate to https://github.com/a-parhom/LightlyShaders
Set to branch „v2.0“
In Konsole install needed packages for building

sudo apt install git cmake g++ gettext extra-cmake-modules qttools5-dev libqt5x11extras5-dev libkf5configwidgets-dev libkf5crash-dev libkf5globalaccel-dev libkf5kio-dev libkf5notifications-dev kinit-dev kwin-dev libkdecorations2-dev

Download and build Lightly Shaders
git clone https://github.com/a-parhom/LightlyShaders
cd LightlyShaders; git checkout v2.0
mkdir qt5build; cd qt5build; cmake ../ -DCMAKE_INSTALL_PREFIX=/usr && make && sudo make install && (kwin_x11 –replace &)

Navigate to System Settings -> Workspace Behavior -> Desktop Effects
Enable Lightly Shaders
Change the settings to
Radius 10px
Shadow offset 6px
Check Outline around window
Outline strength 30%
Check Use black border (dark theme mode)