There are solder pads which marks S5 or S6 on some flight control. S5 stands for UART6_TX and S6 stands for UART6_RX, they are a complete set of UART port, which can be used to connect receiver, VTX, GPS, or other devices.
Some customers said that they are unable to use UART6, and there are only UART1 and UART2 in Betaflight but no UART6 option, as shown in the below pic.
Please copy and input following CLI command in CLI tab to enable UART:
resource MOTOR 5 NONE
resource SERIAL_TX 11 B03
resource MOTOR 6 NONE
resource SERIAL_TX 12 B10
Note: SOFTSERIAL1 stands for UART6_TX and SOFTSERIAL2 stands for UART6_RX