To calculate 7MCS, or the Wi-Fi connection quality score between 0 and 11, 7SIGNAL needs four parameters: channel width, spatial streams, data rate and connection type (PHY).
However, Android 10 does not expose the connection type (PHY) through their API to third-party applications, like 7SIGNAL. When connection type (802.11ac or ax) is not available from the device, 7SIGNAL cannot determine 7MCS.
As a secondary option to obtaining the connection type, 7SIGNAL refers to the connection type broadcasted by the access point. If it is a Wi-Fi 6 (802.11ax) capable AP, then 7SIGNAL uses this value for the PHY. But when the data rate and the PHY are not aligned, then 7SIGNAL cannot calculate 7MCS. Refer to the MCS Index for reference.
Starting with Android 11, devices deliver the connection type (PHY) to 7SIGNAL, which allows the software to determine 7MCS.