Running 11.0.1 I was able to play multichannel FLAC files on my Raspberry Pi 4 over HDMI to my Audio Video Receiver.
After upgrading to 11.0.3 only the front channels would play. My receiver was showing all five channels coming in, but apparently some kind of downmixing to the front channels is occuring.
I reinstalled 11.0.1 and everything is working fine now.