Last thing is to open up the source block (the menu in this case) where the anchor is.
Final result, the anchor you put is: blahblah otherwise #blahblah as you prefer.
When you create smooth scrolling to custom blocks / addons:
you think of a name like: My Custom Block
1. In the source block, as anchor you put: my-custom-block
2. In the destination block, as ID you put: my-custom-block
You have now created the link between source and destination
your smooth scrolling to custom block now is working