Legacy portals are supported. However, it's highly recommended to upgrade/migrate them to interaction portals.
The legacy portals continue to be included with Pega Customer Service and will be available for some time. While you are encouraged to move to the new portals, they are not a requirement for upgrading to Pega Customer Service 7.1.3 or later versions. However, most of the UI investment is focused on the Interaction Portal and Account Manager Portal, and support for new features in Pega Customer Service or the Pega 7 Platform might be limited or unavailable in the legacy portals.
Please go through below links, which talks about the advancements and process to upgrade.