Just using some of the example code, I have everything working fine on an Arduino Uno. I try doing the same thing on a Adafruit Trinket M0 (SAMD21) and the code runs, but the output pins act strangely.
For a 4 pin stepper, 2 pins never turn on, one pin is always on, and one flickers an LED dimly and inconsistently. This happens at multiple speeds. Changing the pin assignment changes the glitched outputs, it doesn't seem to depend on the hardware of each physical pin ( the trinket has a lot of multi functionality on each of the 5 available pins ). I looked up how to port to the trinket and didn't see any obvious issue in accel stepper's code.
Oh and the stepper library that comes with Arduino works fine on the Trinket, well mostly fine, I'm trying to make a mechanical clock and I'm running into precision issues, but that probably is a limitation of that driver, as I was having better results with accelstepper (running on an Uno)