Click on the + 1 to James' post at the far right.
View attachment 1189864
He could, but it wouldn't do much good.
If you are trying to advise on how he can mark the thread solved, you'll need the next button down.
But because you are not the thread creator, you won't be able to see it. ie. other users can't mark other people's threads solved (except for moderators)
The upvote/downvote thingy is actually the least effective thing of all the things you can do. Because liking a post is a better way or saying thank you than clicking upvote, as it has no real impact other than to say "yes, I agree with the answer given".
Supposing someone has a post that has a rating of -1 or less, it is essentially saying "that's a terrible answer, you clueless individual".
The upvote/downvote comes into its own on stuff like whether you think it is an AI image or not. Someone could say "I think it's AI" without being totally sure. Other users could then upvote it as if to say, yeah - you're right... whereas if people thought it was real, they could downvote it to say "nah, it looks real - what are you talking about?"