We use Discourse at Nextcloud a bunch – so first thanks a lot for that great open source software.
A colleague just said that I should look at a specific thread that they @mentioned me in. I let him know I didn’t get a notification and only after some time we found out the reason was that it was a private message.
Hence it would be cool when a person who @mentions someone in a private message who is not part of that conversation gets prompted if they want to invite that person. Of course not automatically invite them, but a nudge would be a good UX improvement.
An overall improved visual indicator as linked to above nicely covers this use case as well as others, so let’s take any further discussion over there.