AR doesn't have the same learning material as machine learning as a lot of the technology was developed in the private sector as apposed to academia. I've started this Coursera specialization - Extended Reality for Everybody. It covers VR and AR. Course 1 - overview, course 2 - design, course 3 - development. To get an idea where the tech is at you will have to start developing prototypes with the different SDKs. It's not easy as documentation is sparse.