Translation - Japanese: USC-シリアル：CDC下でのUARTフロー制御 – KBA230578 - Community Translated (JA)
Why does UART Flow Control not work for USB-Serial Devices configured as Communication Device Class (CDC)?
Native Windows/Linux/Mac CDC driver does not support UART Flow Control for the USB-Serial devices.
The Hardware Flow Control feature for UART is a custom implementation present in the Cypress CDC driver (CypressUsbConsoleWindowsDriver64). To use the feature, the USB-Serial device must be bound to the Cypress driver.
You can install Cypress CDC and Vendor driver for USB-Serial devices from the SDK installation available at USB-Serial Software Development Kit Page.