I had the same issue on my UX550 until I activated two bottom speakers.

apt install alsa-tools-gui

hdajackretask

Select a codec: Realtek ALC295

Click Show unconnected pins

Then you need to override Pin ID: 0x1b and Pin ID: 0x1e and select Internal speaker (Back) or Internal speaker (LFE) - I didn't noticed any difference between them.