S.Bus and S.Port are both inverted protocols. That relates to what is considered 1 or 0 a high or a low. The Frsky Standard is inverted signal levels, but in Frsky words its of course "uninverted".
So any Input-pin that is supposed to accept SBus or S.Port has the correct inversion so it works.
Ports that are multi-functional (like the SYS port on Spirit or Copter flight controllers UART) dont have this inversion. Some processors (F3, F7,H7) have a built in inversion that can be set by software. But others dont have that.
Frsky aknowleded that some time ago and offered pins where you get the "uninverted" signals for SBus and Sport/Fport. Well, Frsky sometimes calls this inverted SPort. And now you have all the confusion that is needed...
So, from my point of view:
Spirit doesnt have a software inverter. So you need a hardware inverter (the integration cable) or you have a receiver with an "uninverted" S.Port pin. R.XSR e.g. also have a tiny tiny pin for that.