Ignoring your rant, AudioServerPlugIns are (and remain) supported, but there is next to no guidance on how write (or debug!) them.
You can either bite the bullet and start from scratch, go with NullAudio (or the C++ SimpleAudio (?) variant that uses the CoreAudioHelper classes) — both of which are old but can be brought forward reasonably easily —, or look for a different starting point.
There's different open source projects that have working AudioServerPlugIns, for example SoundFlower, BlackHole, BackgroundMusic, or SoundPusher. A commercial solution (which you may be able to license) is Rogue Amoeba's Loopback.
q-p
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