Just search for “amd hdmi 2.1 linux” to get full story.

In short - AMD wrote an implememtation for HDMI 2.1 standart for Linux driver, but it requires approval from HDMI consortium. They (consortium) denied it, so AMD couldn’t ship it.

Take a look at HDMI versions in wikipedia and select cable accordingly.

Don’t go with “cheapest” advices as you might buy cable that only capable to FullHD@30Hz, which I think not what you want.

Also, if your card and TV have displayport I’ll suggest to go with that instead of HDMI. It just better and does not forbid open source realisations, like HDMI consortium does on HDMI 2.1.

They’re in wiki markup by default. Markdown is a separate plugin IIRC.