If it's meant to not work, why is it there?

i don't know why it's there, but no, it's not meant to do anything. only mods can lock threads. maybe it works in forum groups so that the owner/admins can lock threads within that group, but i've never actually tried it.

Yep, as the owner of a forum group I can and have used it. Of course it only works in my specific group and not in the forums in general.

If you want a thread locked, you can edit the title by clicking on it to change it to say (or to include) "lock please" or something similar. Then if a minimod sees it, they'll lock it for you