Before Enabling Voice Processing:
<AVAudioFormat 0x600001a69180: 1 ch, 44100 Hz, Float32>
After Enabling Voice Processing:
<AVAudioFormat 0x600001a5bb10: 9 ch, 48000 Hz, Float32, deinterleaved>
As you can see, enabling voice processing significantly alters the audio format of the input node. In my case, the channel count increased from 1 to 9, and the sample rate changed from 44100 Hz to 48000 Hz. This change is consistent with the behavior mentioned in the StackOverflow post.