I knew how to do this with the previous viewing permission function... but now, how do I limit the view for some Promapp users to just a particular folder? i.e. all of my internal users (ALL STAFF) are able to see all the folders, but I have some external users who I will want to exclude from ALL STAFF (if possible) and limit to view only a few folders.
Under the new permission structure it would be really tough to accomplish what you are aiming for. All users are included in the All Staff, and if you were not to use that role to give what use to be the General Permission it would take more effort.
It is easier to use the new permission structure to restrict certain folders from general users. There is currently no way to remove someone from the All Staff system role. So if you did not want all Users in your Promapp site to see all general content you would have to maintain a separate role (Internal and External Users??) and use that to grant access to the general pop and have a more limited one for what you are looking for. This would be a lot of work.
Depending on how you have done the config for minimode it might be easier to share the folders you want with those external users using minimode links. You can use a minimode to share a group, but that would only work if these external users are not needed to own/create content in these folders.