> I'd like the audio input to be able to pick up desktop sounds on MacOS the way it works on Windows.
Even paid apps like Wirecast are having a hard time figuring out a workaround for that. I ended up using Loopback from Rogue Amoeba ($99), and it does the job absolutely beautifully. You configure your Mac's audio output to point to Loopback (which shows up as an audio output device), and then you use your broadcasting tools to use Loopback (which also shows up as an audio input device). You can do mixing, too.
FWIW, I was unable to get Blackhole working reliably (having dealt with this problem several times on Windows, Linux and Mac in the past). It seems very sensitive to which devices are being used in aggregate audio outputs. Might be MacOS's fault, but in any case it didn't work very well when I tried it.
I took a quick look at the issues list & features request, and I'm going to disagree with you there. For example, you can't route the output to different monitor devices and change their volumes. (I often use my headphones as a mixing monitor.) It looks like a neat free alternative, though.
Even paid apps like Wirecast are having a hard time figuring out a workaround for that. I ended up using Loopback from Rogue Amoeba ($99), and it does the job absolutely beautifully. You configure your Mac's audio output to point to Loopback (which shows up as an audio output device), and then you use your broadcasting tools to use Loopback (which also shows up as an audio input device). You can do mixing, too.