You seem to have an undertone that if one belief of Catholicism is false that means that religion is untrue. I am unsure on this, and if any one has any thoughts, please chime in.
It may not matter to a person who has rejected Catholicism, but there can be genuine curiosity or a desire to understand a religion’s teaching.
Also I am Catholic, so I want to know my own religion’s teaching, as well as curiosity for other’s sake.
I think what @redcatholic is pointing out, is that Catholicism is either all true, or not true at all. Catholicism teaches that it is the one Church, founded and preserved by God Himself, who protects her to infallibly teach truth on matters of faith and morals, and not to bind the Church to belief in error.
There’s no wiggle room for picking and choosing which
official teachings are true/false. Either they’re all true, or else anything that’s true would only be coincidentally true, like a broken clock is right twice a day.
It’s important, of course, to distinguish between Tradition and tradition. And between official unchangeable teachings and mere changeable disciplines. Etc.
But if we come across any particular teaching which the Church asserts we
must believe, and we categorically refuse to assent to it? There’s an underlying issue there. Because in that case we would not just be refusing assent to one teaching: we’d be refusing assent to the whole underlying belief that the Church has authority to teach.
Now, we don’t have to
know every teaching. And we’re allowed to ‘wrestle’ with teachings (the name Israel itself means ‘He who wrestles with God’). But while wrestling, we still have to
assent to each teaching, even before understanding why it’s true. It’s commendable to go through and learn why it’s true (and that can actually be really important for helping others, through apologetics and evangelization!) – but for each of us the first step is at least to be able to say that we trust that the Church is who Jesus said she is, and we trust that the Holy Spirit is protecting her as Jesus prayed He would. Details are details, but that’s the starting place.