Not sure if this will help you or not, I’ve got RSSI feedback from the X8R receiver to the Taranis X9D+ via the normal FrSky telemetry, then used this to put the RSSI back in a transmitted channel back to the receiver for display on a minimOSD. In the minimOSD (nightghost version) I just designated the RC channel with RSSI and it’s displayed onscreen OK.
The reason I went with this round-about method is I have a Pixfalcon, so limited inputs and outputs, but 16 channels available via the X8R. I only have 1 telemetry port, so I can only hang one device off it , or potentially 2 - a telem radio and OSD provided they both use the same protocol. So I cant use an OSD or telem radio AND a FrSky adapter.