When Catholics use the word tradition with respect to revelation, they mean all and only those things which Christ taught the apostles and commanded them to hand on, and which are called public revelation - that is, what Christ revealed and which His Church has always taught, faithfully, since it’s founding.

An obvious problem for those who want to have a Bible without a church’s authority backing it is not having any way to determine which books are or are not inspired by God, without essentially becoming their own pope (at least for themselves).

The reason it is essential there be a clear teaching authority for safeguarding and handing on faithfully all of Christ’s teaching is that otherwise you have some admixture of error, and who can resolve which is authentic vs just someone’s opinion. Thus we have 30,000+ different Protestant denominations, all claiming they are teaching only what is true, yet one can find disagreements over virtually every point of belief, including very important matters.

When Catholics use the word tradition with respect to revelation, they mean all and only those things which Christ taught the apostles and commanded them to hand on, and which are called public revelation - that is, what Christ revealed and which His Church has always taught, faithfully, since it’s founding.

An obvious problem for those who want to have a Bible without a church’s authority backing it is not having any way to determine which books are or are not inspired by God, without essentially becoming their own pope (at least for themselves).