>>8128165Well...
for example, to achieve something similar to that image, you set the taskbar to "Floating", set it to the top of the screen and make it a bit narrower. Play around with the things that are displayed on the taskbar (icons in the middle, etc). You can do all of this with the options by right-clicking on the taskbar.
For the windows, you want to have a look around if there are themes that give you the look you want. You don't have to adopt a complete theme, you can mix and match window decorations, colours, plasma design, etc.
The desktop in your image also doesn't have buttons to minimise, maximise and close a window (most likely the user uses keyboard actions for that) so you have to experiment.
The rest is icons, fonts, and maybe choosing software for its look.