https://wccftech.com/hdmi-2-1a-to-get-new-standards-for-next-gen-hdmi-displays-including-source-based-tone-mapping/

We recently reported that the HDMI Licensing Administrator stopped labeling newer HDMI displays with the 2.0 version, and allowed manufacturers the ability to utilize the HDMI 2.1 moniker, as long as it fits the standards already set. This potentially can cause a manufacturer to label an HDMI 2.0 display as the 2.1 version to falsify claims to consumers and was seen by a Chinese seller practicing that exact scenario.

Now, there is a new HDMI 2.1 variant about to be released at some point in the future with the moniker of "HDMI 2.1a."