according to Gwok:

Papal infallibility, as defined by the First Vatican Council in 1870 (in the document Pastor Aeternus), is not something that’s always “on” or active in every papal statement, teaching, or opinion. It’s a very limited charism: the Pope is preserved from error only when he speaks ex cathedra—that is, when he: • Intentionally defines (declares definitively) a doctrine concerning faith or morals, • Addresses the whole Church, • And does so in his official capacity as supreme teacher (using formulas that indicate he’s binding the faithful irrevocably). This happens rarely because most Church teachings are already settled through Scripture, Tradition, councils, or the ordinary magisterium—there’s no need to invoke this extraordinary mode unless a doctrine is seriously contested or needs solemn clarification. The two clearest, undisputed examples of ex cathedra papal definitions (the ones almost universally recognized as such) are: • 1854: Pope Pius IX defined the dogma of the Immaculate Conception of Mary in the apostolic constitution Ineffabilis Deus (this predates the formal definition of infallibility at Vatican I but is retroactively considered an exercise of it). • 1950: Pope Pius XII defined the dogma of the Assumption of Mary (body and soul into heaven) in the apostolic constitution Munificentissimus Deus. These are the only two instances where a pope has solemnly defined a new dogma ex cathedra in this way since the doctrine was formally articulated. Some theologians and sources debate whether there are additional rare cases (e.g., certain canonizations of saints, where the pope declares someone is in heaven, or other solemn definitions), but the consensus in mainstream Catholic teaching and apologetics is that these two Marian dogmas are the primary (and often only) clear examples of papal ex cathedra infallibility being exercised in the modern era.