It is possible, but generally a Bad Idea™.
If they’re wired in series to ensure they have the same current = torque, then the power supply voltage will be far too low for the motor driver to manage the current for correct microstepping.
If they’re wired in parallel, then the motor driver must supply twice the current to achieve the same torque. Unfortunately, single-board GRBL-ish machine controllers typically have small stepper driver chips with maximum current less than you’d need, with barely enough heatsink capacity for the normal currents.