This my main gripe.
As of now, PG forums has the most public information on support for SecureBlue from what I see (aside from what the offer on their mainsite and FAQ, which is decent).
But also in the age of LLMs, a public forum is now prone to getting absolutely slammed by bots scraping for content, so now walled gardens actually have a distinct advantage sadly.
You can have content online in 2 ways:
The 2nd is what a documentation should be written in and is not a problem being blasted with bots, it’s pretty much free to access an .html file rather than generate it on the fly like this forum.
Moreover, even if you do SSR you still can have some proof of work or other kind of captcha to kinda keep the bots at bay. Let’s just not enclose ourselves into platforms just because of bots.
Moreover, it’s not like Discord, YouTube, others are fully bot free either. 
If people stick to Discord it’s for the ease of use + networking effect mostly, not about DDOS concerns.
A forum is dynamic content and is not static files. SecureBlue already has a static site which can easily utilize documentation.
Hosting your own forum also means securing your own forum infrastructure atop of moderation. SecureBlue does not need to secure Discord’s infra, they just worry about moderation. This is another task for a lightweight team to manage. Its not just ease of use + networking, there is also maintenance of maintaining ones own infra.
This does not mean I’d prefer they stayed on Discord, but providing context as to why SecureBlue may not be jumping ship from Discord right now.