Ah ok I thought it was on vps.
From the google search console you should already see if their crawler can access it/if there are any errors, if you already have an account... otherwise you have to add/verify the website to your account first.
Go check what it says about the website there before making changes. Maybe it's something else.
If you tell me there's already a sitemap with all the forum categories, then it's just a matter of making it accessible to google.
(what is generating that sitemap would be the question? maybe you already installed some module to do that time ago. Or it was included in the ISP version of mybb... could see the modified date on the file if it's getting updated automatically...)
There's also that thing about missing meta tags like description, but since it requires modding the page/templates parts of mybb just forget about it for now...
it was very important years ago... these day google should generate the description once it's able to crawl the content, like other search engines are already doing...
It's like it can't crawl the content AND it's missing both the title and description tags, so it really doesn't know what to put there...
https://www.google.com/search?q=site%3Am...m&filter=0
also it's trying to crawl the /archive/ and other paths that could generate errors/duplicates, there should be a better robots.txt more specific to mybb than the one you have now.
You could integrate yours with, for example, this one from the google seo plugin github:
https://github.com/frostschutz/MyBB-Goog...xample.txt
or this one
https://community.mybb.com/thread-111191...#pid868252
naturally use the correct the forum path.