I can confirm the following working (RC and Telemetry using Yaapu9 Lua on Taranis) :
Pixhawk4 + Frsky RXSR (ACCESS - F.port firmware)
The RXSR is straight wired from S.port pin to Tx on Serial4 (no juggling around with non-inversion pins on receiver). SerialX_OPTIONS=7 does the trick here.
I still have the problem that Telemetry does not recover after RSSI reaching low value (not determined the threshold yet). When signal strength recovered, only the receiver based telemetry (RSSI and RxBT) are coming back up. This was also the case in S.Bus + Frsky passtrhough, not related to this F.port implementation.
Let’s have it ! One wire less !