MacOS doesn’t even have per application volume control, which is a crazy thing to say for the OS aimed at audio professionals (at least as far as I know.)
But I don't think that's a feature requested by audio professionals. They're working within applications, not playing audio from multiple apps at the same time. And it would be extremely annoying to discover that your DAW output volume had accidentally somehow been set to 90% and you hadn't realized it. I mean, mixing is done with visual decibel meters, but a lot still depends on little details that are above or below the threshold of hearing, which an application-level volume control would mess with.
I can’t believe that only a few people have ever asked for a way to mute an app entirely.
I grow weary of excuses around the lack of a built-in feature for this. “Apple doesn’t want to do it” is the only reason.
But if Blackhole does what you need, that's awesome!