I had seen someone used that "solved" thing the other day and thought it looked very interesting. It is a Discourse plugin:
https://github.com/discourse/discourse-solved
I investigated and discovered that it's currently configured in a manner that requires it to be enabled for each forum category individually, and it was not enabled for this category. I have now enabled.
Yes, I think so. I can only see it on my own topics.
@sterretje please check if you see the "Solution" checkbox at the bottom of the posts now that I have enabled it for this category. It should be as shown in this screenshot:
