Thanks @robert!

A follow-up question. Is wpForo only auto-generating og:image based upon the first post? Because it's not generating anything for  https://www.macobserver.com/community/mac-questions/turn-off-ignore-accidental-trackpad-input-and-other-annoying-features/ and there's definitely an image in the answer there.

Yes, it only checks the first post as the topic text. Other posts are just replies. We may consider to make it looking into other posts in future. I'll update this topic once we added that in our to-do list.