Great question as I recently had the same. Here is what I received from ANYCUBIC on Amazon:

"Thanks for your attention to Anycubic Brand. In fact, the D version is an upgraded version of the C version, and the D version adds a strain gauge protection pad for protection. Now we sell almost all D versions, which is also an improvement based on market feedback. The best way to distinguish is to look at the S/N code. If the 7th digit is the letter D, this is the D version. If you want to buy, please visit this link, it is our latest version: https://www.amazon.com/dp/B08LZ21MV8?ref=myi_title_dp "

Version C is the 3rd generation and version D is the 4th. I placed an order using the link they provided. Currently waiting for mine to arrive, hopefully it is the latest version. When I had reached out directly through ANYCUBIC (their site) I was told they sell both. This made it sound like a luck of the draw.

Hope this helps!