Backstory
This thread suggests pacmd list-sinks and switching to a different sink with pacmd set-default-sink "SINKNAME", but my laptop only appears to have 1 sink, so that didn't help me.
This thread suggests pacmd list-cards which shows hdmi-output-0: HDMI / DisplayPort right at the bottom of the output, and that looks right, but it still says Failure: No such entity when I run pactl set-card-profile 0 output:hdmi-output or pactl set-card-profile 0 output:hdmi-output-0