As my ubderstanding, RTS/CTS are used for HW flow control of UART communication.
RTS will be asserted (pulled low) when it is ready to send data and will be deasserted (pulled high) when it finishes the transmission.
For DE(Driver Enable), it seems HIGH to allow data transaction and LOW to disable, which is opposite as how RTS works. You can just add a inverter between RTS of UART from Jetson and DE port of MAX22500e
Please also share the full dmesg for further check.