Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
I have just now been added to my packs Scoutbook as a den leader and den admin. I can see the scouts in the den, but when I try to access advancement (or most other things) I am brought to a page saying I don’t have Scoutbook Plus access. Under connections manager it says I have full control.
I was a den leader a few years ago with a different pack and at that time had no problem editing advancement.