The XM+ puts out RSSI signal on channel 16 (AUX12 as first 4 are your AETR)
-Go into the top-right corner of your Betaflight receiver tab and set RSSI Channel to 12
-Go to the OSD tab and make sure the first slider, RSSI Value, is enabled
-go to the Setup tab and on the right side, RSSI value should be showing