RECOMMENDED: Click here to fix Windows errors and optimize system performance
If you notice that there are missing applications in the volume mixer, here is something you should look at. Volume Mixer & Control in the Windows operating system offers better graphic displays and the ability to control the volume of all applications that require Windows 10/8/7 audio support. With this new mixer, you can adjust the volume for each application separately. To access it, click the speaker icon on the right side of the taskbar.
Applications missing in volume mixer
Open control panel > Sound.
Double-click the speaker/headphone icon to open the following window :
Ensure that applications can take exclusive control of this device.
If this is not the case, select it, click Apply > OK and exit.
Restart your computer and check.
Hope this helps!