Its HDMI forum issue. Because AMD want to implement in their Linux drivers (which are open-source). But HDMI forum do not want them to become open source, see related issue: https://gitlab.freedesktop.org/drm/amd/-/issues/1417

In fact, AMD already invested several months in fully testing and developing 4k 120Hz. Its possible, but the HDMI forum people are blocking this, because the HDMI forum has the latest saying.. Its all about money this world. And the HDMI forum is evil.