Postpartum rehab can be for a variety of reasons.
It can be for pelvic pain, pain with sex, sciatica, incontinence, back pain, neck pain, diastasis recti or pain with exercise.
Depending why you are going to postpartum rehab, what you do there will look different, but these are all valid reasons to seek out rehab.
If you are going for back, hip or neck pain the therapist should assess if there are tight muscles or weak muscles somewhere and give you stretches and strengthening exercises to help. These may include postural exercises.
If you have diastasis recti, rehab should be very specific exercises to improve your core strength and help heal the stretched and separated abdominal muscles. The exercises a person needs to do for postpartum therapy, whether or not they had diastasis recti, should start with working on engaging the deep abdominals and not necessarily going for difficult abdominal strengthening such as planks and crunches.
If you need pelvic floor therapy for pelvic pain or incontinence then the therapist will likely do a pelvic exam, but looking at the muscles of the pelvic floor and not looking at your cervix or uterus like the doctor is looking at.
This video gives an overview of what pelvic floor therapy looks like on the first visit.
Your body after being pregnant goes through many changes and all birthing people deserve postpartum rehab, even if you have no specific complaints. I especially encourage moms who want to participate in high intensity exercise to get postpartum therapy. Exercise is great, but the wrong exercises too soon postpartum can cause other issues.