Hello @Tom248,
Yes, it is, to put it mildly, very unprofessional of Airbnb to change the interface and then to be not in the least bothered to update their help articles. They neglect this aspect of their operations again and again and aparently have no intention of putting a process in palce to take care of it as there is a history of it for the 15 months that I've been on this forum.
To find the badge to embed HTML for your listing, reviews etc. click on your profile photo and then on "Account settings" in the drop down menu. Then click on "Badges" on the left.
Then click on your listing photo.
Steve.