If it's for a specific niche, probably best to contact newsletters or news sites about that niche, and try to get them to feature it, that's better than showing something to HN or similar sites. If you pick news outlets targeted at your subject area you get a specific audience who is already interested in your idea and is a much easier sell, and you might get far more useful feedback - you want to talk to potential customers ideally. You don't say what you want to showcase, it might help if you did as then people could give specific suggestions.

If it's Go related (written in Go or about Go), it's welcome at https://golangnews.com