I’ve got the “KiwiEars AD1” USB-C DAC dongle to work reliably on the Jolla Phone 2 for sound output (sounds good for in-ear-monitors, but it does have a fragile cable), after creating a symbolic link to a config file, executing those commands in the terminal:
cd /etc/pulse/xpolicy.conf.d/
devel-su ln -s usbaudio.conf.disabled usbaudio.conf
I could not test controls or microphone as my headphones have neither.
Link to the product: KiwiEars AD1 | Premium DAC Adapter Cable for High-Resolution Audio