They were always mostly for other startup people so were never that useful unless you were targeting other founders.

Medium is definitely outdated. The interface is just so hostile that it seems most credible authors have moved away by this point. The average writer is probably on Substack or a blog at this point, and the average startup founder is probably over on social media.

ProductHunt? Probably also outdated, though in large part because of how cliquey the site is and how hard it is to get your work on the front page.

Not sure about Indiehackers, since I've not really used it.

Wouldn't say X is where everyone is going though. It's kinda been overrun with bots and spam right now, and a lot of people are trying to jump ship to the likes of Mastodon/Threads/BlueSky/etc. But at the same time, those alternatives are also too small to be really that credible for marketing on as well.

So uh good luck.

The channel definitely depends on the the product/service and where the ideal customer(s) are hanging out.

At an early stage, experimenting is important.

Other channels work well, too, such as Reddit, Youtube, blogs, etc.

compared to others. x has more users and will be seen by more people, reddit is also a good channel but it will often hide your content.

Yes, seems things start/build on X and get spread on other media this days.

As a founder, I have found Twitter to be the most interesting so far and have met great people. Medium is a no go for me considering it is behind paywall. PH for me has always been about cool toys. Fun but nothing serious plus it is gamed these days anyway. IH had a promising start but the quality isn't the same anymore.

What is PH?

What matters is what your users do, not what other startups do. Good luck.