As the topic title suggests, ‘Add/edit link’ keyboard shortcut does not work in Scrivener Composition mode. Also, the option is missing from the right click context menu (text selection + mouse right click).
This seems a minor issue, and certainly I can live with it, but it can be very frustrating to jump back from the composition mode (where I love to write and edit) all the time I want to insert a weblink.
Nevertheless, Scrivener 3.0 is a fantastic tool.