The difference is LMDE uses debian and its packages as a base while the “cinnamon” edition uses Ubuntu as a base. I believe they both actually use cinnamon as the DE.

It’s more of a just in case because a lot of the linux community isn’t like Conical lately.

It’s the same Debian base under the hood, but has:

• A more user-friendly installer (I know Debian’s has improved with Trixie, but Mint’s is still easier IMO).
• A newbie friendly welcome screen that walks them through setting up a snap shot back-up tool, theming, updates, firewall, as well as easily providing a link to help documents, and shows the user the software center exists.
• The excellent Mint Software Centre Appstore (I don’t think that comes with Cinnamon on a standard Debian install, I think it’s just the terminal).