Most French verbs are conjugated with avoir as their auxiliary verb in compound tenses and moods, and therefore do not require agreement with their subjects. But avoir verbs do need agreement in a very specific construction: the past participle must agree with the direct object when it precedes the verb.
All pronominal verbs are être verbs in compound tenses and moods like the passé composé, which means that the past participles must agree with their subjects - at least in theory. In fact, it's not quite so straightforward.
Qui n'a jamais vu, ne serait-ce qu'une seule fois, dans des atlas géographiques ou des manuels d'histoire, l'imposante majesté de l'Arc de Triomphe de Paris, sur lequel débouche la magnifique avenue des Champs-Élysées, et dont l'allure caractéristique représente si bien la France ?
Although the subjunctive is commonly used in French, there are numerous ways to avoid it, with varying meaning changes. (This doesn't mean you don't need to know how to use the subjunctive, just that there are times when an alternative is acceptable.)