I have never had any luck sealing gypcrete. Portland based products won't normally stick to it.
My uncle, told me 50 years ago that gypcrete was never intended to be used for floors. He worked in a place making the stuff. It was only supposed to have a 30 year life span. Then contractors discovered if they used it for floors, because it was so much lighter than concrete, they could save millions on structural support. and money rules over common sense.
One of the apt complexes where I did flooring, had 1/2" plywood decking and 2" of gypcrete for the floors. It was broke up into little pieces, so we covered it with Kangaback carpet so they could be rented. You could still feel the stuff move around under the carpet.