Thanks for your reply!
Here is how I assumed it works, :
USB: USB == SERIAL0 == SR1
Uart1: VTX == SERIAL1 == SR1
Uart2: RX == SERIAL2 == SR2
Uart3: CAM == SERIAL3 == SR3
Uart4: --- == SERIAL4 == SR4
Uart5: ESC == SERIAL5
Uart6: GPS == SERIAL6
So my assumption is that my RX (ExpressLRS receiver) is on SERIAL2 so we need SR2_x
In one of my tries I tried putting the SR1_x and also SR4_x to 1 but it didn’t change anything… now I think about it I’m not sure if I rebooted that time.
Is there documentation for this? (I searched, but probably used the wrong keywords 
)