Hi @salenthouse, Do both you and your friend have the latest crossplay version installed of Age of Empires: Definitive Edition? If your friend is on the old client you will not be able to see each other’s multiplayer lobbies. More info about updating the old Microsoft Store client to the crossplay version here: Upgrading to the latest Age of Empires: Definitive Edition (Windows Store)
You may need to reinstall Xbox Gaming Services to address the message you are receiving on your PC. Instructions on how to do that are here: https://support.xbox.com/en-US/games/game-setup/troubleshoot-games-windows-10