"What are you crying for, Windows 10 piece of shit settings app that doesn't understand how to let me control individual sound devices the way I want?"
i have a shortcut on the lower-right of my desktop called "real windoze sound settings" (linking, of course, to the actually useful windows sound settings) for exactly this purpose xD
You need EarTrumpet! It replaces the janky windows 10 sound thing with a more modern (and actually useful) one. There's also a registry hack to just enable the old one that opens mixer, if you'd like.