I actually think there's a few things at play with two-footedness. Whether you can physically do it, whether you're confident doing it and whether it's instinctual or not. Most professional players probably have one out of those three when they could/should have two. It's certainly very rare to see players like Greenwood who have the lot.
The ability to manipulate the ball well with either foot is a skill like any other and it's certainly coachable to an extent. At this club we've seen Charlton and Ronaldo hammer a high level of it into themselves in their late-teens through sheer graft. Hell, training twice a week at the bottom of the football pyramid around age 17 I coached myself to be pretty two-footed despite being utterly left-footed as a kid. Similarly, confidence with using any learned skill comes with practice and experience. There's no reason why a professional footballer should feel the need to check back onto their strong foot when there's a perfectly easy weak-foot pass on. Hitting that very low bar would be a drastic improvement for most of our players and it's very achievable, which is what I meant in my initial post.
What sets Greenwood apart is that he's naturally two-footed in the sense that in a high-pressure situation where you or I would hesitate to use our weak foot, or perhaps instinctively lead with our strong foot regardless of whether it was the best choice at the time, he wouldn't have that split-second mental block. That's clearly not coachable, which I probably should have made clear from the start. It's also made it a lot easier for him to gain the ability and confidence others need to work harder to attain.
@TrustInJanuzaj - tagging you here because I hope this clarifies what I mean.