This function resets the CP210x TX/RX FIFO when opening or closing the COM port.

When the COM port is closed before the data received from the USB Host (PC, etc.) has been sent from the UART side, or when the COM port is closed before the data received from the UART side has been sent to the USB Host. , the unprocessed data will remain in the FIFO as garbage. If COM is reopened in that state, garbage data will be sent, which may cause application problems.
The Flush Buffer feature allows you to reset the FIFO so garbage data is no longer sent.

The figure below shows the setting screen in Simplicity Studio (device is CP2102N).