With regard to Marco Polo I suggest reading/audible the original (1957ish English for example). Imprisoned, he had his notes and memories and there is history about contemporaneous and near contemporaneous acceptance. The book reads like a travel diary and does not read like it was particularly made up. But numbers of the stories he relates are second hand.

As a window on the world at that time, I think it is no worse than say any newspaper in regards to truth. It is the opposite of sensationalistic and mostly dry with too much correct detail to be second hand. As Andrei says, read it for yourself. I did, and think it very nice. Same goes for many books. Gibbon, for example, must inevitably be full of falsehoods, but is largely correct and tells a real story overall which is worth reading and cannot possibly be called a lie.

QAnon thinking needs evidence of intent. Marco Polo does not have that. The others Andrei mentions do show or reveal intent.