There are such groups on Discord. :) Also, some excellent YouTube channels dedicated to the art of the craft. And of course SubReddits. This specific forum, for the Marketplace, would be where you might ask for help finding a battlemap, token set, adventure, or product otherwise available on Roll20 to buy for your game. They just don't really have a space here for general craft discussion. It's about Roll20 or go elsewhere, seems to be the general attitude. Very targeted. Fortunately you will find if you search that there are many excellent communities with DMs as the focus. The closest you might get here is the occasional looking for group ad to specifically link DMs with DMs for brainstorming and practice. You may be able to make such a personal connection here, if you wanted to work with a DM over Roll20 to hone your skills together. This particular section of Roll20 is useful for talking about assets that already exist or seeing if someone knows about one you haven't been able to find, or asking for someone to make something that definitely doesn't exist yet.