my single pole dimmer has a hot (black), white (neutral) and green ground. The new dimmer appears to require a hot, neutral, ground and load.... why, don't get it?
Your old dimmer had neutral, eh? Now think that through.
Let's see. We've got safety ground; then always-hot as supply; then neutral to power the device -- Wait, aren't we missing something? How does it power the light???
The answer is, that wire you have identified as neutral, is not neutral at all. It is surely switched/dimmed hot to the light. The old dimmer does not need neutral to power itself; it's designed to get power by leaking it through an incandescent bulb. This is the old way of doing things, and it does not play well with LED.
Now, I seriously doubt the old dimmer had a white output wire. What I suspect is the wire in the wall is white. That's bad news: it means your wiring the is an old-style switch loop which is using white as a hot wire. That style of wiring does not have neutral. You cannot use that smart switch here, unless you want to pull a /3 cable into the wall and wire it as a new-style switch loop.