I'm working on a hobby design in my spare time that uses a Teensy 4.0 in a EMI/RF sensitive application.

With regard to *unused* pins, would you:
(1) Tie them directly to ground (and set them to OUTPUT and LOW in the startup code)
(2) Tie them to ground through a series resistance
(3) Leave them floating at DC, but bypass them to ground with (for example) a 10nF or 100nF cap
(4) Leave them open
(5) Something else

The PCB is 4-layer: Signal, GND, +3.3V, GND (plus a few signal routes on the bottom)