[andrewmackrodt]

For Netflix at least, you can receive 1080p under non supported configurations by using a browser extension. Last time I checked, non-os default browsers are always 720p, which includes Google Chrome. There are extensions for Firefox and chromium browsers for 1080p playback. However, 4K is limited to Edge on Windows and Safari on macOS.

I may be missing the intended point, but AFAIK neither Windows nor Linux support HDMI volume control (I use all 3 regularly, but only Windows and Linux over HDMI). My Nvidia GPU is connected to a 4K 120Hz TV using HDMI for audio, the TV volume controls are independent of the OS volume settings. Unless OP meant macOS doesn't allow setting the volume independently of the HDMI device.