First off; there is a gigantic difference between the HDMI 2.0 and HDMI 2.1 standards and cables, so if you have a HDMI 2.1-enabled TV or monitor... it's very, very different to a HDMI 2.0-enabled TV or monitor.
HDMI 2.1 is capable of up to 4K 144Hz through the single cable, where HDMI 2.0 taps out at 4K 60Hz -- a very, very big deal for high-end monitors and TVs. But now the HDMI Licensing Administrator has just opened up the floodgates to all monitor manufacturers using "HDMI 2.1" on their displays when they're not capable of HDMI 2.1.
Xiaomi's new 24.5-inch 240Hz monitor was the first spotted with "fake HDMI 2.1" that just launched in China, and while the marketing materials don't push HDMI 2.1 too far, it is mentioned in the specifications with an asterisk. The only thing that this "HDMI 2.1 monitor" supports from the feature set of HDMI 2.1 is support for the TMDS signaling protocol (which is, funnily enough, part of the original HDMI 2.0 spec) but it doesn't support FRL (Fixed Rate Link) which is needed to hit higher bandwidth -- and because it doesn't -- there's no support for higher refresh rates at higher resolutions (you know, like 4K 144Hz as I mentioned above, because 4K 120/144Hz requires HDMI 2.1 and that's the big, big difference).
- HDMI 2.0 no longer exists, and devices should not claim compliance to v2.0 as it is not referenced any more
- The features of HDMI 2.0 are now a sub-set of 2.1
- All the new capabilities and features associated with HDMI 2.1 are optional (this includes FRL, the higher bandwidths, VRR, ALLM and everything else)
- If a device claims compliance to 2.1 then they need to also state which features the device supports so there is "no confusion"
The HDMI Licensing Administrator replied to an email from TFT Central, asking WTF is going on with these whacky HDMI 2.1 specs on non-HDMI 2.1-capable monitors. We are now going to see a world where HDMI 2.0 is no longer supported, all monitors are listed with HDMI 2.1 and no one gives a fuck.
People are going to walk into a store and buy a new HDMI 2.1-enabled monitor, plug it into their GeForce RTX 4090 or Radeon RX 7900 XT of the future, and not be able to enjoy anything higher than 4K60. Even if their flashy new $200 "HDMI 2.1" cable says "up to 4K120 and 8K60 supported" the MONITOR will not, even though the monitor will have a HDMI 2.1 sticker on the box.
What a mess.
But then we move onto resolutions and refresh rate improvements on HDMI 2.1 being not the only thing worth mentioning, because HDMI 2.1 has a bunch of stuff that are great leaps over HDMI 2.0, especially for gamers. HDMI 2.1 includes HDMI Variable Refresh Rate (VRR), Auto Low Latency Move (ALLM), and Advanced Enhanced Audio Return Channel (eARC).