Books

I say "amateur" in the sense that they're free, tend to be released a chapter at a time (which means sometimes series go unfinished if the writer gets bored), and typically aren't connected to a publisher. The writing quality itself can vary significantly with experience though, ranging from beginner to expert. Tbh, the ones I've listed are a lot better than 90% of the "professional" books I've read.

First Contact (by ralts_bloodthorne) and The Deathworlders are absurdly long at this point, so if you're wanting something to keep you occupied for a long time, check those out.

Transcripts is very unique, and while the writing isn't the best, it's very wholesome. I don't know how much I want to reveal, except that the differences between aliens and humans are "all in your head". It brings up a number of subjects I haven't really seen pondered in scifi, like how would an alien society with a significant empath/telepath population (significant enough to require telepathic translators) handle emotional outbursts? What are the moral issues of using cloning and gene editing to create individuals for a specific purpose in a society that is highly advanced in biotech but never figured out silicon? What if the society no longer has the base gene code for their member species because their previous masters destroyed it all in an act of spite? Are living machines morally acceptable?

Like I previously stated, They Are Smol is a shitpost and a good one at that. The first book is a little rough and the second one (the prequel aka the invasion of earth) has some serious emotional whiplash. However both are worth reading and written fairly well, just don't expect 10/10 writing. The companion series, The Smol Detective, is a bit more serious but still kinda silly. It spoofs a lot of detective stories like Columbo, Sherlock Holmes, etc.

Regal Legal Eagle's stuff is stellar, on par or better than pretty much any scifi I've read or watched. That said, Billy-Bob Space Trucker is his first book and is a bit rocky, especially at the beginning. However, it's still worth reading for going full 'MURICA (written when "'murica" was a funny meme and not, "oh god what is going on").

Debris is good and uses scifi as a lens for our current political climate (a human testing the first ftl capable ship experiences unexpected speeds and finds himself hundreds, if not thousands, of light-years from earth. He's rescued by an alien freighter along with the debris of his craft, which is where the story starts). I wouldn't say it's really treading any new ground, but I'd say it's still worth reading.

I can provide links if you'd like!

Edit: I also wanna say that /r/hfy stories (the good ones a least) tend to be a lot more... Colorful? Like, First Contact for an example, plays with the idea that humans, having become incredibly technologically advanced, only die if they have to. So stuff like Star Trek, Star Wars, Warhammer40k, Bolos, etc, are all semi-canon within the First Contact universe because different communities have reserved planets, stars, sometimes entire stellar clusters, for the purpose of LARPing these series with real weapons, full governmental systems, etc.

Like, something about a lot of hfy series tends to make them feel more real and engaging, whereas I've found a lot of published sci-fi works tend to end up feeling a little dry and humorless. Like, scifi is super serious business and we can't discuss serious topics with a humorous tone.