Meta announced that users on Threads will be able to see fediverse replies on other posts besides their own. In addition, posts that originated through the Threads API, like those created via third-party apps and scheduling services, will now be syndicated to the fediverse.
You should just join an instance that blocks threads.net. Fortunately there are many of such instances. Your current instance doesn’t seem to defederate any other instance, which is kind of suspect on its own.
SDF is a very hands-off instance. I’ve seen many trolls in bad actors on there. It also has some management issues since it can go down for long periods of time.
The only reason I have an account there and the only reason I would encourage anyone to use it is because it’s run by the SDF foundation and it will probably be around forever. Well at least as long SDF itself.