Ubuntu 18.04: Put window into screen corner

After writing the question, a similar one popped up: Resize 4 windows to occupy the screen without overlap on Ubuntu 18.04

The keyword was "tiling" and the GNOME extension ShellTile does exactly what I was looking for.

GNOME Extension of preference for me is: Put Windows

It's supposed to be a replacement for the Unity functionality you mentioned.

Use ShellTIle

First enable extensions with: (the prefix chrome is not related to chromium, it works on any window)

sudo apt install chrome-gnome-shell

Then go to ShellTIle

And click ON