Flat roof leak at seam to wall

Flat roof is coated with white acrylux paint. Paint has failed at seam from sunlight over years.Fixed crack with homedepot black roof cement.Can I clean and repaint over black roof cement??? I want to repaint entire roof with roof mastic then roof paint.

You could, but it would not be an effective repair.
Install a new flashing ply against the wall.

Is the paint peeling off or is it wearing off?

If it is peeling off, then you need to get all of that paint off first. Do not use the product called “Cool seal”. This product peels off in a short order.

You want a paint that wears off.(i know that sounds funny)

It sounds like you have gotten some good advice from a good roofer. Stick with that advice.

The correct term is called "roof emulsion"
Then you paint it with “aluminum roof coating”.
Your roofing supplier will ask you “fibered” or “unfibered”. I like to use fibered although they say the unfibered goes further.

you can paint the tar,
give it a few weeks to harden up, then it will take
a couple coats to get black tar white.