I’m new too and also have a Mastodon account, just tried my first post on Mastodon and was able to see it here, just be aware that mastodon post shows under microblog.
Haven’t tested the other way posting here and checking on mastodon but I guess if you post as a micro blog it will show but something under magazines maybe not.
Also want to mention that at first it did not show up (granted was just a few seconds, a minute at most) but I search my mastodon account here in kbin and it showed there and after that it showed on microblog, I guess with the search a kind of forced the sync between kbin and mastodon.
Just tested the other way, posting in kbin and it almost intermediately showed up in my mastodon account feed. But this reply does not show up, so I guess threads do not get shared/synced ¯\(ツ)/¯
edit: Just checked and I see this post on mastodon if I search for you @sotired, but the replies does not show on the feed as are show under the user post and replies tab, I guess mastodon feed only shows posts