Hello,
It’s my first post and I am sorry that it’s not something that helps others rather asking for help. 
We have been using our installation of Discourse on our local server for internal communications for two years. And we like it a lot.
I find Discourse’s topic link preview(Onebox?) one of the best features of Discourse and it has been working great until I change all the categories permission to the same private(closed) group only removing “everyone”.
I had to do it because we’d like to invite guests to a specific category and we did not want them to see all our internal channels.
I understand that I will not be able to see the topic preview if the security group is different.
But all our category has the same security group called “our company name”.
But still, any topic link except the ones that belong to the same category is not working.
Will that be any way that we can have the topic preview feature with the category not open to “everyone”?
I think I extensively searched the forum but I could not find the topic with the same issue. 
I saw the post above but the problem is that my category A and category B has the same security group. but it’s not just public.
By the way, I think Discourse is the best solution available not only for the public forum but also for internal communication. In my opinion/use case, it’s better than Slack or Teams. We had used both solutions for years especially Slack since it was beta, We switched to Teams from Slack for a while and have been using Discourse for 2 years now.
Thank you for developing and open-sourcing this great solution.
好处是它也能保持其格式。
