Not sure exactly what you’re asking, but it’s opt in.

So since I opted in, my mastodon account is shown as a bluesky account on bluesky.

But I can only follow bluesky accounts from mastodon if they’ve opted into the bridge, which seems to be a decent number, but still a small proportion. And the replies to my posts that are on bluesky, will only be visible to me from mastodon if the people replying have opted into the bridge.

I’m not using mastodon much anyways, because there are too little people there who care about what I post, but I use a service to post which automatically posts on mastodon / bluesky (and until last week when i opted out, twitter), so I’ll still be posting to mastodon even though it’s only for a handful of people compared to my 8k bluesky followers.