I have tested this on a DJM750K, 750Mk2 and 900NX2
I have the latest firmware and drivers and have gone through the security and privacy checks and all fine.
I am streaming a set using sites like MelonApp (but doesn't really matter which sites) and need the input device to be the mixer (through the app).
The mixer is seen in sound settings as a USB input and output, but is not recognised as an input in the browser.
If I use an application like loopback (at $100 for full license) I can connect the mixer to work so it is clearly possible with some midi connection hack.
I also tried using this with LANDR and get the same result, their tech support are blaming Pioneer firmware.
Is there a way to get the mixer to be seen as a USB device that essentially acts as a microphone and therefore is seen in security and privacy settings as a microphone so that it is picked up in the browser?