does the test ask questions about Transit Gateway?
it’s not covered in the course
Transit Gateway has been out for about 1.5 years now in GA. It may very well appear on your exam so you should know what it is but probably not worry too much about the details of implementing it for the PSA exam. Customer feedback hasn’t really suggested this was an oversight for the effectiveness of the course.
I would however expect it to be well covered on the Networking Speciality exam though.