Alternatively, you can write an article which would be interesting to the audience (then have a backlink to your product) - which you can submit as a regular post. E.g. your product is an A/R app for interior design, you could post a medium article about how you wrote / coded the A/R feature. If it's interesting it could get upvoted to front page but again, HN is super technical so unless it's good it'll be brutal

For TC etc you can try cold emailing (you'll need a press kit etc) but if you have contacts and a unique angle you'll get more success. But TC usually not the best place to launch unless your audience is there - you migth get a big bump but then will drop off dramatically after