Agile Coaches are for those teams who want to improve and adopt new agile ways of working and more progressive mindsets, but have decided not to use Scrum (for whatever reason).
Scrum Masters have a first class place in teams who have decided to follow and use Scrum, and defined in the Scrum Guide.
Scrum Masters don’t have a place in a team that doesn’t use Scrum.
Sounds simple, doesn’t it?
Beware of being hired as a “Scrum Master” into a team where Scrum is not being used, has been discounted, is not known about (believe me, this actually happens).
Usually this is a big red flag, an indication of a possible agile anti-pattern and team dysfunction.
Ask any project manager about the key to their success, and they will say that delivering a project is often more like a "dark art" or by chance, than a predictable science.