Teensy 4.x / IMXRT1062 - max output current
I think you are misinterpreting the datasheet. That Imax is how much current the GPIO is consuming. Because it's CMOS based DC current is negligible. Higher data rates increase current consumption.
I looked through the datasheet and did not find an absolute max GPIO output current. For what it's worth tables 26/27 mentions GPIO output impedance.