Iris VS audio-router

Iris Shaders + Sodium - Link - Indium - Link - (Indium is needed for many other Sodium based FPS increasing mods) - Increases performance and shaders performance

You can install iris from here: https://irisshaders.dev/download and they have a complete installation guide here: https://github.com/IrisShaders/Iris/blob/37f491553cea26241a8561da90917c740d7a573c/docs/guide.md

Downloading the latest version off of the official Iris website or GitHub should be safe: https://github.com/IrisShaders/Iris/releases

Audio router

I imagine Audio router might help in what you're looking for.

The ones that people recommended that I could still find (both of which are at least 7 years old): https://github.com/audiorouterdev/audio-router https://vb-audio.com/Cable/index.htm

I personally use Audio Router, you can look up guides about how to set it up fairly easily.

How did you used to route audio from YouTube to Audacity? Mac's require something like Blackhole to do that. Maybe try something like https://github.com/audiorouterdev/audio-router

https://github.com/audiorouterdev/audio-router and some virtual cable device?

If Voicemeeter can't force it, you can use this one, so you can select the output for the specific app. But you'll still need Voicemeeter or Virtual Audio Cable

One program you can test is Audio Router. It can't mess up anything, but it also has not received any updates in over 6 years so it's not uncommon for it to not work with certain devices or programs.