there seems to be a bug with file attachment in permission management. It's only possible to upload files if in the users usergroup the option "Dashboard - Can edit member" is activated. If it is not, the attach file dialog is not available.
Screenshot attached. Versions: wpForo 1.6.1, WP 5.2.2.
Thank you for using wpForo and for contacting us!
No, the permission doesn't have any relation to Attach file button. wpForo has a built-in spam control system. It controls newly registered users and allows to attach a file when a user has X number of approved posts. 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.
Ah OK, works perfect. Needs some time to understand all options. 😉
Thanks a lot!