How can I map certain solution articles to a specific product portal?

In Freshdesk, you would have the option to create multiple portals, from the Estate Plan onwards. Under Admin > Channels > Portals and Select the Portal of your choice and you would find the option to associate Solution and Forum Categories to specific portals alone, using which you could make the solution articles from that category to be displayed on the corresponding Portal.

Furthermore, the visibility of the articles can be defined on a folder level under the Solutions tab.