HDMI is a confounding mess of standards and ports, with many aspects left to the discretion of manufacturers. Even while HDMI 2.0 can support 4K at 120Hz, not all HDMI 2.0 TVs and consoles are capable of doing so. It appears like another HDMI upgrade is on the way.
The new HDMI 2.1a standard will be announced during CES 2022, according to The Report (the HDMI Forum has yet to reveal anything). The most important new feature of HDMI 2.1a is Source-Based Tone Mapping, or SBTM for short, which offloads some HDR tone mapping to the video source (e.g., your console, set-top box, or PC) rather than the TV or monitor doing it all on its own.
In addition, the functionality would make it easier to mix HDR and SDR video on the same device. You could, for example, be using a video editor that is rendered in SDR but has HDR video thumbnails and previews.
A new page on the HDMI Licensing Administrator’s website discusses the additional functionality, even if it doesn’t expressly mention HDMI 2.1a:
Source-Based Tone Mapping (SBTM) enables the source to send a video signal that takes full advantage of a specific display’s HDR capability by adjusting its output to take better advantage of each display’s potential. As with other HDR technologies, rather than adopt a fixed set of color and brightness ranges, SBTM allows the Source to adapt to a specific display. SBTM can also be used by PCs and gaming devices to eliminate manual user optimization for HDR.
The new SBTM functionality is supposedly optional for device manufacturers to incorporate, so there’s no way of knowing for sure unless a TV, monitor, console, or other device specifies it supports SBTM – even if it claims to support HDMI 2.1a. Next week, during CES 2022, keep a watch out for the first items to support HDMI 2.1a, which is gradually becoming an online-only event.