Thank you for your suggestions and insights!
Noticed that actual professional modelers use Air-brush on varnish. And that is what I am aiming at to get me self.
Sorry cant be of more help.
I guess that airbrushing is way more controlled than with a rattlecan, but since I don´t own an airbrush this is no option for me,
atm. I want to see how much involved I get into the hobby before upgrading my gear.
Closest equivalent I've found in rattle can is Mr Hobby's Super Clear (the brand has a variety of finishes in matte, satin, and gloss, Super Clear is the matte finish)
If I´m not mistaken, Super Clear could lead to problems with the acrylic paint, and "Topcoat Matt" or "Premium Topcoat Matt" from Mr. Hobby is preferred. But the article I read this from was about protecting gunpla figurines, so it might be different with painted minis.
Right now I´m thinking about trying a mixed approach, with a matte brush-on varnish for more control over pooling/ avoid frosting, followed by a light spray of matte (Mr Hobby, maybe) to reduce the satin effect, if necessary.
Rattlecan should still be more appropriate for sealing pigments on the bases and such, rather than brush-on varnish.
I guess the only way is to try it out on spare minis to find the best working method for oneself