Move Window by clicking on any part (as on Linux)? On Linux (or X in general), it's possible to move a window while holding down a modifier key (Alt+drag or Super+drag) and clicking on ANY part of the window.

This makes moving windows super easy, as one doesn't have to aim so well ;)

On macOS (High Sierra), this doesn't seem to be enabled/possible by default.

How do I enable this or what add on do I need?
You can use the free utility called "Easy Move+Resize", which allows you to use Cmd + Ctrl + Left click anywhere inside a window to move it. The modifier keys can be customized so that you can choose for example Alt + Left click instead.

You can download the utility from here:

https://github.com/dmarcotte/easy-move-resize

Read under the heading "Installation".