I have a Corsair K70 Lux. It has a mute button.

When I have a Youtube video playing on Chrome, and when I press the mute button on my keyboard, the muting works fine but it has a weird side effect where some internal setting in Youtube changes. Specifically, the size of CCs changes to 50% which is very annoying because I usually have CC open. Pressing the mute button again does not revert this setting. I have to manually click in the Youtube video's settings and change the CC settings.

I don't have hope that raising this to Youtube would get this fixed so I was looking to fix this locally for myself. My very broad questions are:

1. How do I identify what is the keycode of specifically the mute multimedia button on my keyboard? I am aware of the usage table in usb.org but I don't understand the difference between System Speaker Mute and Keyboard Mute and which one is used by my keyboard (it does appear to do a system mute where it acts as the usual Windows 10 multimedia control with the little multimedia window popping up each time).
2. Where do I begin in implementing something locally on my Chrome to disable reading that specific multimedia key? Would it be a Chrome plugin and what do I have to learn for that?