I didn't realise I use this regularly, but now that I'm on macOS, I'm now aware of this tiny, but useful feature of X11.
You can get X11-like move window by clicking anywhere on it by setting
this flag true:
$ defaults write -g NSWindowShouldDragOnGesture -bool true
and then logout and in again.
It's <cmd> + <ctrl> + <click> rather than <alt> + <click>
but close enough.
