We can use command
pactl - Control a running PulseAudio sound server on terminal
first, list our available properties in our machine using this command:
pactl list cards
based on my hardware above, i set output:hdmi-stereo as my default profile using this command:
pactl set-card-profile 0 output:hdmi-stereo
if we want to set to internal ...
This seems to be a limitation (bug?) of the current sound setting app. The current workaround is to install PulseAudio Volume Control from the AppCentre, and to select a HDMI configuration profile.
Related Stackexchange Issue
Related Github Issue
I'm facting similar issues on HP Spectre x360. Loki worked great, but Juno is terrible.
In response to Unable to disable built-in monitor, I have found a way to turn it off:
Find out the display names:
xrandr | grep conn | grep -v dis
Disable the desired display:
xrandr --output <display> --off
On my machine, first command returned: