I found that the wav inference with stt indeed blocks the node.js event loop for the inference duration so nothing else will be happening while transcribing.
The same is not true for the stream class. The transcribe stream function is by its nature non blocking. So if you plan on transcribing multiple things at the same time i would recommend to look at the streaming transcription.
At least thats my experience. But worker threads should work too in theory.
Johannes