The same fix had to be done for the fmu-v5x: PX4/PX4-Autopilot#14932
@ -258,6 +258,7 @@ CONFIG_UART4_TXBUFSIZE=1500
CONFIG_UART5_IFLOWCONTROL=y
CONFIG_UART5_OFLOWCONTROL=y
CONFIG_UART5_RXDMA=y
CONFIG_UART5_TXBUFSIZE=3000
CONFIG_UART5_TXDMA=y
CONFIG_UART7_BAUD=57600
CONFIG_UART7_IFLOWCONTROL=y