Is it OK to Use Liquitex Matte Clear Coat with Black 3.0?Updated a year ago

No it's not. You can't use any kind of varnish or topcoat over Black 3.0. There's no material out there as matte as 3.0 so anything you put over it will add sheen and make the surface smooth and a bit shiny. It can also sometimes causes white marks. I understand people really want to make 3.0 durable and to protect it but sadly that's not really possible, things painted with it are delicate and decorative. However we are working so so hard on the durability and I feel like later this year we will have a tough as nails durable version.

If you really really want to you can but it will sacrifice the black effect.