Q1:
According to WP76 product technical specification, UART1_CTS is output pin.
And if you see the wiki page here about DTE/DCE, the CTS pin for DCE is output pin which means that the WP module is regarded as DCE device.
However when you do the open UART port process in linux application, it will regard the device to be DTE, that is why you need to switch the naming in order to do what you want on CTS pin.
Q2:
“gpiolib-sysfs.c” did not change the behavior of CTS RTS.
So it is not related.
When you do the open UART port process in linux application, you should be able to choose the flow control setting.