real time audio stem separation is already possible, some specific models can even get around 20ms latency (HS-TasNet) https://github.com/lucidrains/HS-TasNet

There was a nice paper with an overview last year too https://arxiv.org/html/2511.13146v1 that introduced RT-STT which is still being tweaked and built upon in the MSS scene

The high quality ones like MDXNet and Demucs usually have at least several seconds of latency though, but for something like displaying visuals high quality is not really needed and the real time approaches should be fine.