Doesn't exist.  At least not for eBay type auction, and even the one centralized marketplace that was like a classifieds (or eBay's Buy Now),  ... Paid.co, has gone defunct or otherwise requires a shitcoin token now (Stacks), I believe.
 
You can see some reasons and some other good discussion on the topic here:

*Why did OpenBazaar Fail?*
https://stacker.news/items/38688

Your own e-commerce site where you accept LN payments is possible .. using BTCPay Server, and other tools.

earnbitcoin

Plebeian.market
Also there is some other platform just can't find a link rn.
But not decentralized that's for sure. 