I am not able to submit URLs
I am not spamming. I have a 7-year-old account and have posted only one post that is 7 years old. I was trying to post a github repo link.
The old article might have been auto-killed because it was from a green account and had the same subdomain as the user's HN account. Back in 2017, that might have auto-killed it. Not sure it would kill it today. But it might.
In theory, there might be a minimum karma to post URLS. The official HN FAQ only notes a minimum karma to be able to downvote. There are unofficial FAQ's, but I pay too little attention to be able to recommend one.
1. Look at articles on the front page, pick out a site which frequently gets articles there
2. Look at 10 or so articles from those sites and pick the one you like the best.
3. Post and see what happened.
But the subdomain matches your user name and your account does not have a history of engagement with HN (irrespective of its age). That may correlate with low quality content in general and threrefore there might be a "self-promotion" heuristic in place.
It's not that self-promotion is banned on HN. But using HN only for self-promotion is generally discouraged (or explicitly discouraged) because it sucks up oxygen without much benefit to the community.