I know this is something that has been requested in the past. Turns out it’s a default plugin for Discourse. The original poster and site staff will now be able to mark solutions. You can see an example in this post.
I have enabled this feature for the following categories:
- PowerShell Help
Posts in these categories will have a small box next to their title. If the post has a marked solution the box will be checked, otherwise it will be empty.