Essentially, would a modern English speaker be able to converse with a Middle English speaker, in theory.
Hi, the question of "how far back could I go and still communicate in English" is a popular one in this sub. Please check out this recent post, and do please follow the link therein to a few more on the Middle English period
Some of this would depend on the speaker of Middle English. Chaucer wrote with a London dialect, which was the ancestor of the main, conventional stock of modern English. Even so, much of Chaucer's vocabulary and his pronunciation would make communication a profound challenge.
That said, it would be more difficult to speak with the fourteenth-century Gawain poet - the anonymous author of Sir Gawain and the Green Knight. That author came from the north of England, speaking a dialect that was removed from the main evolutionary trunk of modern English. Reading that poem, and presumably attempting to talk with its author, would be far more difficult than attempting the same with Chaucer.