We are Canadians, will travel to Portugal (17 nights in Sep) first, then fly from Portugal to Spain (Lisbon to Seville). As there are different answers and confusion wrt SpTH form (is required or not) for people like us - no EU DCC but arrving from an EU country, I sent an email to SpTH (email@example.com). Below is the reply from them:
Regarding your request, if you enter Portugal for two weeks, you will not be asked for a certificate or QR code to move from Portugal to Spain. However, if your arrival in Portugal is only a stopover before arriving in Spain, you will need to complete the form provided for this purpose. I hope to have answered your question.
Gracias por contactar con nosotros, thank you for contacting us, merci de prendre contact avec nous , on vous remercie de nous contacter.
Spain Travel Health