Hey guys, how can I make the "Attach file" option visible when adding a topic using the shortcode?
I'm sorry but I don't follow you. If you mean the "Attach file" button is missing you don't need to use any shortcodes.
wpForo has built-in spam control system. It controls new registered users and allows to attach a file when a user has X number of approved posts. I see the user you check doesn't have a minimum number of posts to be able to attach a file. Please manage this setting in Dashboard > Forums > Tools > Antispam > New Registered user section.
BTW you can set this option 0 if you want to allow just registered users to attach a file
Ok, thank you for letting know we'll check it and back to you asap.