If you want to filter a WriteFreely blog's content by hashtag, you can follow posts that only use those hashtags. All you need to do is take a blog's hashtag url and add "/feed/" to the end.
WriteFreely supports federation via ActivityPub, allowing people to follow your blog from popular platforms like Mastodon (an alternative to Twitter). Learn more about how following works with ActivityPub in the [Federation guide](https://writefreely.org/docs/latest/writer/federation).