I have a BetaFPV Meteor65 Acro with a built-in DSMX receiver. I'm wondering if the F4 1S Brushless Flight Controller V2.2 (DSMX) supports RSSI. I've seen DVR of people flying and they have an RSSI value on the OSD but mine just flashes 0. I checked the product page for the quad and the FC that is in the quad and I do not see anything mentioning RSSI. Maybe this is not supported with an FC with a built-in RX and only supported with an external RX.
Most serial receivers support RSSI through a feature called RSSI channel.
This means, unlike in receivers with a dedicated RSSI output, you can map one of the channels to carry the RSSI signal.
For example, on a FrSKY receiver, the telemetry channel is channel 16, or aux 12.
So you would go into the receiver tab in Betaflight and set RSSI channel to aux 12, and then place the RSSI icon in the OSD.
It is likely a similar process for Spektrum, so I would recommend consulting your transmitter’s manual.