Is it true: John Paul I sudden death (Sep 28 1978)?

There's no solid evidence for it.

The claim is that John Paul I was murdered, usually said to have been poisoned, by P2 and Vatican Bank figures to stop his reforms, and that the Vatican covered it up. That claim is unsubstantiated. No toxicological, documentary or eyewitness evidence of poisoning has been produced, and Yallop's specific supports have been challenged on the record: the 4:30 a.m. discovery time his scenario needs, his premise that the pope was in perfect health, the 'missing' personal effects, and a motive that rests on a conversation nobody else heard. The nuns who found him, the Vatican doctors' records and a chest-pain episode the evening before point to a natural death, whether a heart attack (the Vatican's finding, restated by Stefania Falasca in 2017) or the pulmonary embolism John Cornwell proposed in 1989. The true part is the context: no autopsy was performed, the Vatican first wrongly said his secretary found him, and the P2 and Vatican Bank scandals were real. With no autopsy and no exhumation reported, poisoning cannot be excluded forensically, so the claim is rated unsubstantiated rather than debunked.