MirHamid If my English was good I could explain better
No, your point is easy to understand. You're right, it doesn't make much sense to start a discussion in the Solved tag. But you are overlooking a couple of things:
First, the "Solved" tag is not a feature of Flarum. It's a tag we created for discuss.flarum.org; so it's a kind of content. If you don't want a "Solved" tag on your forum, you don't have to create one.
Second, as I explained above, this is not just a matter of design; if you want a "Solved" icon next to the discussion title, you (or somebody) is going to have to create a whole new extension to do that.