Hi, I'm having the same problem, looks that such option to hide the brush stamp (or outline) doesn't exist, which is really frustrating as it's very annoying trying to paint anything with that mark over it.
But what I really don't understand and worries me a lot is the lack of response from the developers. I can see this post is from last year, and not only they haven't fixed it (can't imagine it would be too complicated to do so..) but also they haven't even replied
This definitely puts me off using it, I gave it a chance as a possible alternative to Photoshop but I can see (if things stay like this) there's no way I'm changing..
Thanks