are what the saints say throughout church history infalliable. Like the diary of faustina for example
Don’t get too obsessed with the word infallible. Private revelations are not binding on anyone except the recipient. Individuals can make mistakes, even pious individuals who are later canonized as saints.
Read the Catechism through for a comprehensive summary of the Church’s teachings.
Private revelations such as the diary right through to Fatima are not required beliefs for salvation. Thus the Church does not define them as infallible, as there is no need for such determination. Don’t worry about the concept of infallibility. As one wise post already suggests, read the Catechism of the Church. Here you will find the true teachings of the Church. Here you will find the words of eternal life.