Thanks for the tips here. Could you elaborate on Carla? I tried Googling around but didn't mind much detailed information. I work on Lyrebird so could be helpful as you say.
Carla: https://github.com/falkTX/Carla
It lets me install any normal audio pro audio plugins, for example https://github.com/xiph/rnnoise
It also does some cable management, but qpwgraph is maybe better for that.
I looked at your code and the approach (IMO) is kind of bad.
If you want to solve the problem of "voice changer", you can skip the UI entirely and just use plugin parameters. You can also skip the problem of managing the connections. And when you publish your work, every pro audio software (Ableton, Reaper, whatever) can use your audio processing.
Hope that helps.