It’s a very basic action, but I can’t figure out how to add a node to a way, and then turn it into a traffic signal.
Neither right-clicking on the way were the node should be nor Tools > Add node (requires entering coordinates instead of just clicking on the map) work.
Mouse click on the crosshair shown in the middle between two existing nodes.
Edit: square → crosshair
Found it right before your post: It’s apparently not available in the menu, but found in the *toolbar *: “Draw nodes”, third icon from the top.