If the Knowledge Base articles are publicly hosted and visible to everyone, you won't require a license to view them on the customer portal. However, if there are any restrictions in place, such as articles being visible only upon login, you may need to sign up for a customer account, log in, and then access and view the solution articles.
To check the visibility settings, navigate to Admin>Portals>Settings>Who can view solutions. Adding a screenshot for reference:
In summary, the accessibility of the solution articles depends on the article visibility settings chosen by the Freshdesk account owner. If the articles are publicly available, you can view them without a license. Otherwise, you may need to create a customer account and log in to access the restricted content.