I got a question related to best practices to configure a GPIO if the pin is not used. To make it short, the recommendation is to leave the GPIO floating on the PCB and leave the GPIO in its "Default" state as shown in the Signal Multiplexing table in the Reference Manual. The Default state is either “Disabled” or an analog function.
Some Kinetis devices have analog only pins (PGAx/ADCx) while most have GPIO pins with analog functions (PTx/ADCx) or digital GPIO pins
Unused pins, whether analog only or GPIO, should be left floating. Analog only pins do not have input buffers that will cause shoot-through currents when the input floats. GPIO pins with analog functions default to analog functions, which disables the digital input buffer – no shoot-through current.
The digital GPIO pins default to "Disabled", which disables the input buffers - no shoot-through currents with floating inputs.
Finally, unused pins shall not be tied to VDD or VSS. Hence, when designing your board and there are some unused pins, leave them floating on the PCB and then make sure that the software leaves the GPIO in its Default state in the MUX register.