I am working on KDE plasma 5.
When strike Alt+Tab to switch applications, they are displayed on the left side of the screen.
How could enable them to be displayed on the center of screen like in Gnome?
The Task Switcher settings don't provide such an option.
By
they are displayed on the left side of the screen,
I assume you're referring to something like this:
To change that, open System Settings > Window Management > Task Switcher
In there, there are just too many settings to describe in detail. The video link provided by mook765 goes into great detail.
For your purpose, avoid choosing Breeze or Breeze Dark in the image below.
Whether you wish to have Show selected window checked or not is your preference.
But here are images illustrating the task switcher in the center of the screen. (The images are cropped and don't show the full screen.)
Small icons
Large icons
Thumbnails
Informative
Compact
Text only
There are some related options described in Is there an alternative task switcher to KRunner which is focused exclusively on window switching?.
