Regarding to reference manual, there should be possible to set open drain for GPIO output.
"The device does not support open drain on all the pins. Only pins that are configured for a protocol that requires open-drain(e.g;, LPI2C, LPUART single-wire) will work in open-drain mode." - Chapter 4, Signal Multiplexing and Pin Assignment
If i use GPIO on FLEXIO line it should be possible. Unfortunately, I did not find any register where is possible to set open drain option.
Can you describe this function more to me?