Which scenic areas are must sees for someone going to Portugal for the first time? Is it hard to drive there? Or is it easy to get around with public transportation?

The Peneda-Gerês National Park, in northern Portugal, near the Spanish border, best accessed from the ecclesiastical capital of Braga and best accessed by car, although there may be buses from Braga. It sits 36 km. from Braga.

More info here-
https://juliedawnfox.com/exploring-p...national-park/

The drive is the same as all winding mountain drives, and given its relative remoteness, I doubt that it is readily accessible via public transportation.

https://flic.kr/p/7MXnru

There are small group day tours operated by Oporto Adventure Tours from Porto to Peneda-Geres, but it makes for a very, very long day.
https://www.oportoadventuretours.com.

This explains how to reach Geres from Braga (and yes, there are buses but one would be captive to the infrequent bus schedule).
https://geres.pt/en/how-to-reach-geres/.

So it sounds like it's better to rent a car. Thank you for the recommendation for Geres. Any others in addition?

Geres is Portugal's only National Park, although there are Natural Parks, such as the Sintra-Cascais Natural Park near Lisbon, the Arrábida Natural Park on the Setúbal peninsula south of Lisbon, the Natural Park of the Costa Vicentina on the Alentejo coast, which has wonderfully deserted beaches and cliff walks.

Thank you for the suggestions. We didn't go to Geres. But we did go to Sintra-Cascais, Arrabida, and Alentejo and Vicenti Coast. We loved Arrabida the best, but Alentejo and Vicenti Coast was also beautiful.