I haven’t thoroughly digested the entire encyclical, but I did not notice, nor have heard, that any new doctrine was defined in it. Infallbility is normally associated with the defining of a true doctrine of faith, or a canonization of a saint. When a pope speaks infallibly he says so, and it could be in an encyclical, but usually not. Encyclicals are like letters to the faithful, very much to be listened to. They can contain infallible truths, like any letter you might personally write yourselves, if you are faithfully communicating the truths of the faith. Letters can contain untruths, but not likely in the case of a pope, who has done his homework.
It is not the point to respond to any papal letter with a question of is this infallible or not, but to receive the instruction and exhortation in an open manner.
Mostly, I find encyclicals to be insights, exhortations, reflections, and usually are of contemporary relevence to the faithful of the time, and possibly for future generations to come.