Whether or not the guy historically known as “William Shakespeare” actually wrote all those plays. For one thing, the plays were probably produced with a lot of input and modifications on the fly from the company itself, so already anything that Will himself wrote is going to have been significantly altered along the way.

For another, the historical Shakespeare is almost as much of a folk character at this point as Paul Bunyan, so anything we can “know” about him is what we can reassemble from the historical record after 400 years have passed, so it’s all fairly muddied anyway.

Could just some guy from Stratford have written those plays? Yeah, I think so. Could it have actually have been some nobleman writing under a pen name? Also possible, but doesn’t meaningfully change the content of the plays or my feelings about them. In hindsight, if it was a pen name, the dude probably should have just bit the bullet and published under his own name, because now some glover’s son is the Immortal Bard, and Edward de Vere is the guy that only the cork board and red yarn set care about.