The way I understand the current situation is that the board does have the capability to run ethernet, assuming you also have an external ethernet circuit, and the right software.
I believe the same situation applies to the 2nd USB port on Teensy 3.6.
So the bottom line is the reference sheet is wrong as there is no Ethernet support on the 3.5/6 boards. Probably should update it don't you think?
Teensy 3.6 WIZ850io 1143.58 212.59 ok ok
WIZ820io 1102.71 202.44 ok ok
WIZ812MJ 274.14 180.76 ok ok