Corel Painter 2020 - How to dock panels?

I just got myself Corel Painter 2020 and I am trying to set it up to my preferences.

However, I have problems docking panels to the side of my window. When I grab a panel, e.g. "Color and Layers" and drag it to the edge of the main window, a red semi-transparent bar appears, about 5mm wide. At that moment, when I release my mouse button, the panel returns to the original place where I started dragging from.

What am I missing?