It seems the Scale tool conflicts with the possibility to create prototype interactions.
- Enter Prototype mode
- Activate the Scale tool (K)
- Grab an element’s handle to draw an interaction arrow (eg. Navigate to)
- You can draw your noodle as usual (as when the Move tool is active)
- The handle cannot be grabbed; instead, the whole design element is moved.
If this is an intentional feature then I don’t really get it