According to the mpd homepage, the latest version of mpd is 0.23.15.
13.0.1 appears to be the latest version of some other software called myMPD. The port's livecheck should be improved to return results only for mpd version numbers.
According to buildbot logs, the build failure on macOS 11 is due to the use of kAudioHardwareServiceDeviceProperty_VirtualMainVolume which was introduced in macOS 12, so indeed mpd 0.23.8 is not compatible with macOS 11 or earlier and this isn't in our control. You can check if the latest upstream code still uses kAudioHardwareServiceDeviceProperty_VirtualMainVolume; if so, then it still requires macOS 12 or later and the port should be marked as requiring macOS 12 or later using the platforms keyword. You can file a ticket with the developers asking them to support earlier macOS versions if you wish but they may not want to do that and it's not our job to maintain complex patches for old OS compatibility; it's only our job to offer an easy way to install the software the developers provide.
