Mouse click in interface is dragging instead selecting (Mac)

Hi, I am just doing first steps with blender on my Mac and I am having a hard time with everything because the interface behaves so strange. I left click on any object in the scene collection list and it always gets dragged along with the mouse instead of simply staying selected. Mouse click anywhere also always draws a selection rectangle.

Also anything I click on needs a second until it reacts. For example open color palette of a material. And often having to click someting a second time, after waiting and nothing happens.

I tried with the macbook trackpad without connecting mouse or external keyboard and the same happens. After a restart it seems behaviour is normal for a short time then starts being strange again.

No problems in any other application.

No key active/pressed on keyboard.

Thanks in advance for any input on this.