So it seems to industry trends toward SHIFT for adding whereas CTRL is used for mutating existing elements.

We should avoid the use of CTRL entirely, specifically because CTRL+LMB allows for multi-node selection. We should retain this behavior to allow users to multi-select reroute/knot nodes.

I have a good practical reason for this change: This key bind (Control + LMB) is straight up impossible on MacOS because the OS is hard coded to produce a secondary mouse click event (right click) whenever Control + LMB is pressed. You cannot change this in the OS anywhere, it's just how it works. I currently cannot add knots to my node graphs.

I was looking here if an issue exists for "implementing reroute nodes" and found out that it's already implemented. So why I thought it's not build in? The method is not very intuitive. I'm usually working with Unreal Engine and there you have 2 methods that do not exist here, but are very straight forward: double click on LMB on graph to create a knot or drag and drop a line and write "knot" - it pops up as node inside the list (if I remember correctly, it's also pinned in that box). I think both methods could be implemented in additional here, too. Ctrl+LMB can stay as it is in my opinion. Nothing wrong in giving multiple ways for such an important feature.

The way with drag and drop (or right click to search for) is something playing together with #758 very well and is very beginner friendly. Double click on LMB reduces the hurdle a lot for people coming from Unreal to Godot.