First question: Can someone trace the 0.5 XMR back to my Monero GUI Wallet?
Nope
Second question: Is LocalMonero a mixer/tumbler for XMR coins? If your answer is "yes", I assume that AgoraDesk is also a mixer/tumber for BTC coins?
Both are just p2p exchanges where you can try to buy Monero and Bitcoin using cash or sell off your Monero and Bitcoin for cash without having to worry about KYC or having your funds getting blocked with the excuse of suspicious source of funds.
Bitcoin mixers are completely different, and you can find a variety of them in the service announcements board.