It's sort of a long story... The important thing is that if you have an inverted logic device (like an sbus receiver), you need to connect it to a UART pad that supports inverted signals. On an f4, I think this needs to be hardware inversion. Just check the flight controller manual for what UART to use with sbus and that will be the one.
I'm using flysky ia6b I selected ibus in bf config. My tx in rx select ibus to select servo or hit cancel but it won't select the channel I think. I landed the communicating wire on the pad r3. Using holybro f4 v2 aio
Funny note to this. I got a call from Georgia yesterday from will from Grayson hobby asking about my order of some 28g wire no red only white. My heart was beating so fast I forget my question about flysky ibus and said thank you sir for calling me you are a legend in the industry and an honor to talk to you good by
That combination should work (radio/ receiver). I have it working on my Wizard X220. Gotta make sure the wiring is connected physically to the right port connector on FC. Also, sometimes flashing the firmware on the FC will get the receiver to respond, even though it was bound with the transmitter before. It has happened to me. After that, all worked well.