I've spent an embarrassing amount of time chasing down good collections across different genres, and I've found the trick is to not rely on just one spot. Public libraries, especially larger city or county systems, are seriously underrated for this. Their digital apps, like Libby or Hoopla, let you browse entire curated lists—'LGBTQ+ Historical Fiction' or 'Nordic Noir'—that someone knowledgeable put together, which saves you from the algorithm's sometimes weird suggestions. Plus, it's all free, which is perfect for sampling a new genre without committing your wallet.
Online retailers are obvious, but the secret is in the lists and 'also bought' features. On Amazon or Barnes & Noble, if you find one book you love in a niche genre, clicking through to see what other readers bought often leads you down a rabbit hole of interconnected titles and authors you might have missed. I also adore independent bookstores' websites; many have robust online shops with staff picks sections that are incredibly genre-specific and thoughtful, often highlighting smaller presses.
For really deep cuts, I turn to genre-dedicated communities. Goodreads groups, subreddits like r/printSF or r/romancebooks, and even BookTube channels focused on a single type of book are goldmines. People there don't just list titles; they discuss tropes, rank sub-genres, and share links to author backlists. Following a few dedicated bloggers or reviewers who align with your tastes can functionally build you a personalized, ever-updating collection. My own shelves have diversified way more from following a couple of mystery buffs and a sci-fi critic than from any top-10 list I've googled.