@gawk1873 I've wrote a plugin which may help. You can try

npm install nodebb-plugin-attachment-privileges

This plugin is very simple, it will allow user to view/download attachment only if they have "Topic access" to that category. While using this, you can turn off NodeBB core Private Download function. Because if guest do not have access to that category, it won't be able to access those attachments as well

NodeBB have 1 simple swtich to allow/disallow guest to view uploads, but logged in users will also able to see all. You need a plugin to control that.