I also find this to be very annoying. I usually watch TV through my HD Home Run on a second monitor while working on remote server management tasks over the weekend. I have a few sound output devices on my PC: Bose Speakers plugged in via USB (So they're detected as their own sound card and they're my default output device) in addition to the motherboard Realtek audio and my monitor's speakers via HDMI. If I set Teamviewer to send audio through my monitor instead of my default sound device then it stops muting the channels/apps going through my Bose speakers. Instructions for Win 10 Version 1903: Right-click speaker icon in taskbar. Open Sound Settings. At the bottom click "App volume and device preferences" (oh, make sure you have Teamviewer window open). Use the dropdown menu and change the output device on the Teamviewer app to another output device. I also disabled my Microphone input on my mobo. Problem solved for me.
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