Changes
/* RSSI with FrSky */
* Use this command in the CLI to configure Betaflight to access RSSI, be sure to have the latest version of Betaflight, it varied accross version.
set max_aux_channels = 12 #12+4 = 16 channels
set rssi_channel = 16
save
* You can find official firmware with output on Channel 8 as well (look for RSSI8 or RSSI16)