When I use the search function for topics I'm interested in and encounter Show HN that way, it's dominantly slop (and has been for most of the time I've had an account). The actual Show HN page is not much better.

The submissions that actually get upvoted are indeed pretty good. I think it really is the filtering effect. Standards are whatever, since it's clear that a lot of these submissions are close to one-shot (and even when they would have required some refinement, people don't actually push a meaningful commit history) with an obnoxious LLM house style promotional README.

Often the submission also comes across LLM-generated, including heavy use of Markdown formatting. It gives the impression that people learn that HN is a place to promote themselves, but don't realize how blatantly obvious it is that they didn't actually do anything significant beyond thinking of something for Claude to do[1] and don't care about learning how the site works.

[1] I'm not claiming that work done with coding agents will always be blatantly obvious. I'm claiming that this is the default result for people who don't put in any effort, and lack of effort correlates with lack of understanding.