Upvote:1
Encyclicals are generally thought to be part of the magisterium. They are not weighted as highly as some other documents, and they certainly are not infallible, but given the lack of a higher teaching authority (a council, a papal ex cathedra exhortation, etc), it seems wise to assent to whatever is in an encyclical.
From what I've heard, some theologians are beginning to doubt the authority of an encyclical given how they are being written today. That is: written by a committee of people who are not the pope and merely read and signed off on by the pope himself. But, for encyclicals actually written by popes in prior decades, it stands to reason that what is in them is to be believed unless a document of higher authority contradicts them.
This may help: https://bctorch.com/2020/04/01/a-pocket-guide-for-different-papal-documents/