What platforms are most often used to promote a startup?

Twitter and LinkedIn. I accidentally launched my product, now Afforai is Live 😂😅. It's quite an accident but let's roll it... Would be great if you could check us out: https://www.producthunt.com/post...

If you don't have a big audience on Twitter or LinkedIn - going over at Reddit and talking about your product in its relevant subreddit always works. I made a Tailwind-related product a while ago, shared it on the Tailwind CSS subreddit and got a lot of people to use it, some of them are still using it to this date and its lovely to know. So find the audience that you are solving the problem for, whether its in a Facebook group or a Twitter thread, and promote it there.

hey, I think brand promotion with targeted advertising on Facebook and Instagram

Startups are all over the place. You've got your social media - Facebook, Twitter, LinkedIn. Then there's Product Hunt for launch exposure. Don't forget about Medium for thought leadership, and Reddit for community building.