The "clear teachings of the Roman Catholic Church" are thought up by a small group of male persons and always have been. Women have been completely shut out. There is no consensus among humans as to any of these issues. A separate issue is whether a leader in a democratic republic has any right to dictate his/her personal beliefs as the law of the land without regard to the personal beliefs of the people s/he is leading. Absolutely not.Well, you can join a Catholic parish, get donation envelopes, go to church when the Church says you oughtta, pay a tithe, and call yourself a "Catholic." Being a sinner doesn't enter into it; we are all sinners. Good enough?
But the issue goes deeper than that.
Imagine a "Born-again" Christian who states publicly that he believes that the personage we refer to as "Jesus Christ" is actually an amalgam of a dozen or so messianic figures who all lived around the same time in Palestine, and there is no actual "Jesus Christ," per se. Is this person a "Christian"? [No].
Imagine a Mormon who states publicly that he thinks Joseph Smith was a pure charlatan who made up the Book of Mormon, used his religious stature to screw a small army of women - some of whom were married at the time - claiming to have "married" them to justify his actions. Is he a "Mormon"? [No].
Imagine a Roman Catholic who believes that the morality of abortion is not absolute, but is something for each person to decide, and he enthusiastically supports the right of pregnant women to have abortions. Suppose he also is a firm believer in gay "marriage."
These two positions are diametrically opposed to the clear teachings of the Roman Catholic Church. You cannot be a "Catholic" and hold these views. No conscientious priest will knowingly administer the Holy Eucharist to anyone - especially a public figure - who holds these views. This "Roman Catholic" person is not "Catholic."
Being raised Catholic at the time when Biden was raised, and especially if you went to parochial schools, gives one a sense of "being Catholic," in an intrinsic sense that is comparable to one's race or nationality. The attitude is, "I am Catholic and no one can tell me that I'm not." But that's bullshit.