Current through a Push-Pull Output connected to a Microcontroller
The stepper IC has an SDO support that allows 3.3V interface with standard 5.5V logic impedances.  Historically this CMOS push-pull impedance for 5.5V logic has always been 50 ohms +/-50% and this IC is within this boundary at 5V.

It will be slightly higher than typical at a lower supply voltage of 3.3V.
When operating at the maximum possible data rate for the longest possible cable such as 200 (STP) ~ 240 ohm (UTP) twisted pair, damped edges can be achieved by adding 150 Ohms to the SDO driver Tx to reduce the impedance mismatch which improves data rate or signal integrity and reduces crosstalk as it filters excess bandwidth, associated with mismatch ringing.  (alternatively one could use 50 ohm coax.)

The uC input threshold is near Vdd/2 with recommended limits shown in your question are fine as the load current is always determined by the Rx leakage current (uA) and device input and parasitic capacitance. (Ic=CdV/dt)  (No problem)
You do not have any DC current loading problems whatsoever.
The  concern is for impedance matching on long cables.
Simulation

Same cct at lower SDO clock rate 100kHz on 10m cable

Scope shows direct drive switched to add 150 ohms after mid-stream for comparison of reflections and improved noise immunity.