Is there a way to put the Forum behind a password page that matches their registration password? I will take it off the menu so it's not seen but I'd like to protect it as there will be sensitive content. I've using Divi as the theme.
wpForo doesn't have that kind of option but you can try to find a plugin which can do that, wpForo uses WordPress members, login/reg functionality.
So you need a plugin which will work on WordPress members, login/reg functionality.
Passwords in Wordpress pages just create issues.
Can't you do it with wpForo groups and permissions?