audio-router VS calibre

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.

Not to be confused with Calibre, the excellent ebook software by Kovid Goyal:

https://calibre-ebook.com/

Glad you were able to fix it, but what about trying Calibre? It is free and makes it easy to adjust things, add info, and change front covers.

Or using Calibre (pdf or azw3) https://calibre-ebook.com

There are already some very good ebooks solutions out there so there's really no need. Calibre for the backend and database management, Calibre-Web for the front end, and Openbooks for content.