I will be the first to tell you that the volume mixer never quite worked right. But usually, it was the program missing its volume options on the mixer, or with the Windows Audio service itself that was the problem.
Microsoft says no. And they are axing what I think was the best way to control your audio. By improving it, they insist on replacing everything with their updated Settings panel, which at first glance does not improve very much.
First reported on https://www.windowslatest.com/2018/11/04/windows-10-19h1-update-could-remove-the-legacy-volume-mixer-shortcut/
It will remain to be seen if programs are listed accurately to their audio even working, let alone the device preferences. The launch for this change will be in Windows 10 19H1 Build 18272, and has not yet been released.