I had been having problems getting audio out using a Pi Zero WH & the Adafruit I2S Audio Bonnet using the suggested variable BALENA_HOST_CONFIG_dtoverlay set to "hifiberry-dac”, “i2s-mmap”. I switched to just using hifiberry-dac and now it works swimmingly.
Note this was set using the web interface. I’d previously tried setting these as separate lines in the config.txt starting at line 1067 which resulted in that entire file getting rewritten (odd).
Props to the devs!
Thanks