I'll just reiterate, all it takes is one single piece of large grit in a Scotchbrite and you can ruin your entire paint job.

Flatting agents can be added to any paint to give a matte finish.

For the types of finishes I am most familiar with, you are usually better off using gloss clear coat and treating the finished surface to suit your needs. Gloss usually has a highest concentration of resin.

Another way to get a matte finish is to paint with clear and then sand using that same 600 grit wet/dry sandpaper after painting. You will be able to achieve a uniform luster to the surface.

Another way to get it is to use ground punice and mineral oil as a slurry to break the sheen on the surface.

What material do you plan to use as your clear coat?