The problem with your request is Roman Catholics disagree on which statements are ex cathedra.
Generally there are two that are accepted.
The Immaculate Conception (1854) and Assumption of Mary (1950).
The Roman Catholic has to believe these.
I could make a case for Unam Sanctam as Roman Catholics cite that as a case for having to be a member of the RCC in addition to being subject to the pope....unless they disagree with the pope.
But this illustrates my earlier point.
The laity in Roman Catholicism cannot determine what is or is not dogma. Only the pope can.
As has been illustrated on these threads Rome's dogmas have changed over time. So how can the Roman Catholic know which "tradition" is correct?
This is why the Bible should be the source of truth for a believer in Christ.
The other problem for the Roman Catholic is determining what a verse in Scripture means. Rome has, depending on the source, dogmatically defined between 7-15 verses.
The average member in Roman Catholicism is left with few options other than to believe what the pope is telling them is true. They really have no other option. Else, they are doing exactly what they condemn Luther for.
The Assumption and the Immaculate Conception are ex cathedra, but are in total accord with Scripture, tradition, and reason. The Church has shown this over and over, and there are disproofs too that I can respect. But the main point is: if I assert this and “honor” Mary because of it, I am not caused to be in mortal sin.
Again, the point I’m making is, said in reverse: if a pope says something he claims is ex cathedra that causes people to be in mortal sin, we are not obligated to follow it. The mortal sin will be stark and obvious, because Scripture will be negated and centuries of tradition will have been reversed.