Filigree ceiling and calcium silicate masonry - closing wall-ceiling?

Hello everyone,

we want to paint the wall/ceiling on the ground floor. Simply white. The plaster will be painted, and the ceiling should also just be painted like that.

We have a filigree ceiling and KS as masonry. How can we best nicely seal the joint between wall and ceiling? Acrylic?

As it looks, we have to do this ourselves.

If the plasterer has worked neatly, there should hardly be any joint.