These are my earphones:
Does this link answer your question re TRRS?
My audio settings are default. I didn’t touch anything, other than connecting the mic and cam to the Signal VM (Debian minimal). Mic can and was only be connected to one VM.
DispVM is based on Fedora 34 and has the Zoom video and Firefox where I played YouTube, that send the sounds to Signal.
The built-in mic of Carbon X1 Gen8 does not work with Qubes 4.0.4. I only used the external/connected mic. Internal mic does not pick up any sound.
My assumption is that the earphones are faulty.
I hope this helps. I will try to answer to the best of my abilities.