Hah, I feel like a digital archeologist sometimes trying to find the good stuff without paying. A lot of people will point you to places like Archive of Our Own (AO3) right away, and yeah, the tags there are a godsend. You can filter for exactly the kinks or dynamics you're after. The quality is wildly inconsistent though—some writers are publishing-worthy, others not so much. It's a slog to sift through.
I've had better luck in specific fandom discords, honestly. You find a writer you like on AO3, see if they have a social link, and sometimes they've got whole Google Drives of free stuff they share with their community. It feels more curated. There's also a handful of newsletters where indie authors give away short stories as lead magnets. You gotta sign up with an email, but it's usually worth it for the consistent quality compared to the free-for-all of big sites.