you have the code which says “when target arm length is == 0, use controller rotation yaw, otherwise don’t”
but it is not hooked up anywhere. The arrows represent execution flow. If they are not connected to a function or event, they will never run.
This code is likely intended to run from tick. Type “event tick” and then plug it in. Also try a print string node and plug the boolean in there and you can see if it changes in the viewport while you play.
as mentioned above, there is a new input system, however the old one does remain so you should still be able to follow the tutorial without issue on that front.