What are the effects of backlash from a geared stepper motor used to drive a filament extruder?
During normal extrusion backlash has no effect.
During retraction you can perfectly compensate by increasing retraction length slightly.
Backlash cannot be taken into account for pressure advance, but unless it's a lot, it should not cause issues: pressure compensation is a second order effect and does not need to be tuned super accurately to produce results.
One degree does not seem to be enough to cause problems.