I'm not sure there's any "decentralized" exchange for XMR.
What about AgoraDesk? It supports Monero but I am not sure of it's decentralized nature. They have an arbitration feature but I don't know much about it. LocalMonero is basically the same thing with a different name.
Isn't UnstoppableSwap a decentralized solution for Monero?
Also, Robosats supports Monero. I think it's still centralized, but there was a proposal to make it decentralized. No idea how far they have come with that. If I remember correctly, there was talk about the decentralized solution becoming custodial during trades, so that's not optimal.
These are all companies that charge fees. If their server were to go down, there'd be no way to utilize them. This is the same reason I don't consider something like Uniswap to be a DEX... everyone is dependent on a single server, website, or single point of failure, so they are not decentralized.
An exception to this is ThorChain which utilizes liquidity pools of coins on different blockchains to perform swaps. The fees are paid to the liquidity providers rather than a company.