I see the problem you have. I can explain in a later post. I have built new firmware for you, see enclosed. Please test it as I do not have a board available for testing, and let me know how it goes. If it works for you I will post a pull request to the inav project with the full board. Use your first configuration, set GPS on uart3 (TX3, RX3). Enable sbus on uart6 serial.
inav_2.0.0_OMNIBUSF4V6.hex.zip (284.2 KB)