The short explanation
8K, sometimes written 4320p, holds roughly 33 million pixels per frame against 4K's 8 million. At 60 frames per second with full color and 10-bit depth, that is far more data than HDMI can carry uncompressed — which is why 8K modes always come with a qualifier.
You will see 8K60 4:2:0 10-bit, or 8K30 4:2:2 12-bit, with DSC compression for modes that would otherwise not fit. Those are not marketing shorthand; they are the specific compromises that make the format fit inside 48Gbps.
Where you run into it
Every device in the path has to agree on the same compromise. If your display advertises 8K60 4:2:0 but the chain only carries the capability data for 4K, the source will never offer 8K — and nothing will tell you why.
8K displays are also where the larger DisplayID capability blocks appear, which is precisely where older EDID handling in the middle of a chain quietly truncates what the display was trying to say.
How the DR HDMI 8K handles it
The DR HDMI 8K passes 1500MHz / 48Gbps and supports up to 8K60 4:2:0 10-bit and 8K30 4:2:2 12-bit, plus DSC-compressed formats. Its EDID library includes six dedicated 8K60 4:2:0 FRL-5 tables, all with HDR, three with VRR and three without, in 7.1, 5.1 or 2.0 audio, so you can present a known-good 8K capability set instead of hoping the chain assembles one.
Want to test your own HDMI chain?
The DR HDMI 8K is sold through the HDFury.eu web shop.