Capo's review is correct, but the behavior is not the plugin's fault. All audio sources send their data to a single output unless configured differently. I use Voicemeeter to accomplish that (for very similar reasons), and JACK Audio will also do it.
You need virtual (or hardware) audio inputs and outputs, presented to software as device drivers, to then selectively patch the now separated audio streams into OBS Studio. In the screenshot config, I have operating system default routed through red, games through blue (by in-game config), Teamspeak through green, and mic through purple. They're all audible on speakers/headphones if I want them to be, but you can see in the OBS Studio Settings that OBS never records the operating system default device.
Therefore, this plugin's notification tone doesn't enter the recording, and neither do Windows notifications, music I'm listening to, videos I'm watching, etc.