I always go with discord in newer projects. Why? I feel like most people have discord nowadays and it just works (TM). I rarely have a case where a person said that they can’t join because they don’t have discord or don’t want to create an account because other reasons.
Beside that, money is also a big factor. Slack for example is getting more expensive for communities.
It does not "just work," and you're not going to hear from me because I'm not joining yet another Discord server just to wade through searching through chat. Do a free forum. They've worked for 30 years and I might actually find my answer by Googling and won't need to even making a forum account.
I actually entirely agree with you. Nobody needs to take on accommodations they don't want to. And that was kind of my point; you should be aware that choosing Discord limits your participants and also limits your participants ability to engage with your project.
This isn't necessarily a bad thing; may even be a positive aspect. In a quickly changing project, maybe it's good if your documentation isn't too "sticky" and the solution to a problem isn't low-touch "read the docs" but high-touch "ask me so that I can experience the pain points"
Beside that, money is also a big factor. Slack for example is getting more expensive for communities.