I installed Leap 42.2 with the latest vanilla kernel
(https://build.opensuse.org/project/show/Kernel:vanilla) on a GPD Win.

Its sound chip is a chtrt5645.

It plays sound at the same time on the included mono speaker and the
headphones, and when plugging in or out headphones in the jack I see no change
in the GNOME Control Center's audio output page: it usually displays switch
between "Speakers" and "Headphones", but there it unconditionally displays
"Headphones".

Also, the mono speaker only outputs the left channel.

The expected behavior is to have it switch between either the mono speaker
(playing all the channels mixed) or the stereo headphones when some are plugged
in.