The problem is that HDMI Licensing, a licensing organization for High-Definition Multimedia Interface (HDMI), has declared all new features and functions of the standard to be optional. However, HDMI 2.0 no longer exists; it is now part of the HDMI 2.1 standard.
Thus, even if a device has HDMI 2.1 support, this does not mean that it has received all the new functions of the standard. The manufacturer can simply specify HDMI 2.1 in the context of HDMI 2.0 capabilities. The organization, however, says that if a device claims to be HDMI 2.1 compliant, the manufacturer needs to specify what features it supports to avoid confusion. However, in practice, confusion can arise.
This is what happened with the Xiaomi monitor, which was claimed to support HDMI 2.1. There is a footnote in the specs on the Xiaomi website where it is noted that the device supports the TMDS protocol, but does not support the new FRL. Therefore, now it is worthwhile to carefully read all the characteristics of the product intended for purchase.