Hello po-pony,
I looked for other threads regarding this topic and it seems that there are confusions in regards of the PWM_X pin.
There are only two FlexPWMs on the i.MXRT1024. The PWM_X is not an independent signal, it is an accessory signal, it's rising edge and falling edge are controlled by the VAL0 and VAL1 registers.
PWM_X pin can also optionally output a third PWM signal from each submodule. However, this function is apparently not enabled on the SDK driver, only capture is available.
You can find how this is setup in Figure 50-2 PWM Submodule, on the i.MXRT1024 Reference Manual.

I hope that this information helps!
Regards,
Gustavo