Because the HDMI consortium has members that have an incentive to lock down the standard to enforce copyright. That's how HDMI started to begin with. It was just a DVI-D signal with sound that was encrypted. That's why you don't see TVs with DisplayPort, though I'm going to tryand find one next time I buy one.

Possibly. If you have the option to use DisplayPort instead of HDMI, that should also resolve it today.

I think it also depends on what distro you're using. On Linux Mint Cinnamon, which still uses X11 by default, I haven't been able to use the highest refresh rate of my monitor. But the experimental Wayland support did it without issue.

Later edit: I think you have to compile the whole Linux kernel with the patched amdgpu driver. The GitHub repository for it is linked in the article: https://github.com/mkopec/linux

Edit: I shouldn't comment before reading the article.. This whole comment is irrelevant. Keeping it up for posterity.

End-users generally use the amdgpu driver in the Linux kernel. When it's ready, it'll be merged into the kernel and your next kernel update will have it. If you're on a gaming-targeted distro, they usually get kernel updates pretty fast, so you won't have to wait long after it's ready.

Or TL;DR: do nothing, keep your system up to date, you'll get it eventually!

Don't think so. It's currently focused on 4:4:4 colour at high bandwidth (4k@120hz), HDR, and VRR.

Isn't CEC proprietary and effectively some form of DRM?