Show desktop button Windows 10

You should be able to do that:

https://www.howtogeek.com/howto/28600/move-the-show-desktop-icon-to-quick-launch-or-taskbar-in-windows-7/

Thank you for hint. I tried to make a link and pinned it to taskbar but there was a lag.

The way with Quick Launch bar from your link is better but there is vertical lines on the sides of the button.

So the request is actual. It would be good to add some tiny button half the width of the standard shortcut.

What kind of lag?

Regarding the vertical lines, you can lock the taskbar by right-clicking on it and choosing the Lock option.

Also, you can use the tweaker option to show desktop by double-clicking or middle-clicking the taskbar. You can also use the "Reserve empty space on taskbar" option to always have a space to double/middle click. Refer to the help file for more information.

Lag - delay about a second between clicking the shortcut and action.
Double-clicking the taskbar - I have had this option enabled, but never had a free space to use it.
With "Reserve empty space on taskbar" option it's great stuff. Thank you.