Volume control in Windows 10 Enterprise kiosk mode

I'm setting up a medical device based on Windows 10 Enterprise LTSC, version 1809, OS build 17763.107

It's set in Kiosk mode, so that when Windows starts it automatically launches a custom win32 software. To be more specific, I deployed the kiosk mode via a provisioning profile that I made, very basic, with automatic access, tablet mode enabled, branding neutral set to 32.

Now, in this software we would like to control the audio volume, the programmer tried a couple of different approaches, but none of them seems to work.

I noticed that even if I try to regulate the volume with the buttons on the physical keyboard (which in normal use wouldn't be connected to the machine) it doesn't change. I can ear the sounds, but I'm unable to control the volume

When I run explorer.exe, and the shell pops up, the volume starts to work, both with physical buttons and inside the sw.

So it seems to me that without the default shell Windows 10 is unable to control the volume.

How can I solve this?