During my time testing shimboot on real hardware, I've discovered a workaround to get working audio on dedede, at least through wired earbuds.

Your mileage may vary depending on the adapters/earbuds used, but this is the setup that worked for me:

Accessories
Apple EarPods with 3.5mm Plug ($15.99 on Amazon)
Apple USB-C to 3.5 mm Headphone Jack Adapter ($9.00 on Amazon)

Notably, the EarPods plugged directly into the Chromebook's 3.5mm jack did not seem to work, whereas using the Apple USB-C adapter/dongle I was able to get working audio on dedede (HP 11 G9 EE).

To Reproduce
I have provided a diagram to reproduce the behavior:

This was tested with the prebuilt v1.2.2 image shimboot_dedede.zip available in the 'Releases' section