Hi,
NXP provides MCUXpresso SDK software package for NXP MIMXRT1060-EVK board, which includes Ethernet txrx_transfer demo example with below path:
..\SDK_2_13_0_EVK-IMXRT1060\boards\evkimxrt1060\driver_examples\enet
I find Teensy 4.1 Development Board info here, while NXP does not provided MCUXpresso SDK software package for this board.
Customer maybe could get support from Teensy 4.1 board Forum.
Best regards,
Mike