What is HDMI 2.1?

In plain language

HDMI 2.1 raised the ceiling from 18Gbps to 48Gbps and introduced a new signalling method called FRL to carry it. On top of the extra bandwidth it added variable refresh rate, auto low latency mode, enhanced audio return and display stream compression.

Why it matters in your setup

Here is the catch: almost all of those features are optional. A device can be legitimately labelled HDMI 2.1 while supporting none of them, or while running at 24Gbps rather than 48. Two 2.1 devices can therefore fail to agree on a mode that the specification allows.

What decides the outcome is not the version number, it is the capability set each side actually advertises — the FRL rate, the resolutions, the VRR range. That information lives in the EDID, which is why an EDID readout tells you far more than the box does.

What the DR HDMI 8K does with it

The DR HDMI 8K passes the full 48Gbps / 1500MHz and reports the negotiated FRL rate and lane count live, so you can see which part of HDMI 2.1 your chain actually reached. Its EDID tables let you advertise a specific FRL rate rather than hoping the two ends settle on the right one.