Would the holy Grail be considered a McGuffin?

What about Jason's Golden fleece?

What do you think the earliest example of a MacGuffin is?

In fiction, a MacGuffin (sometimes McGuffin or maguffin) is a plot device in the form of some goal, desired object, or other motivator that the protagonist pursues, often with little or no narrative explanation. The specific nature of a MacGuffin is typically unimportant to the overall plot.

Examples in film include: the meaning of "rosebud" in Citizen Kane (1941),[15] the priceless statue in The Maltese Falcon (1941), the NOC list in Mission: Impossible (1996) or the Rabbit's Foot in Mission: Impossible III (2006),[16][17] the briefcases in Pulp Fiction, several Coen brothers films, and Ronin, the rug in The Big Lebowski, the Heart of the Ocean necklace in Titanic,[18] the mineral unobtainium in Avatar (2009),[19] and the One Ring in the Lord of the Rings trilogy.[20]