Does the Creality Ender 3 allow variable layer thickness?
Variable layer height is a setting of the slicer, not an ability of the printer itself.
However, the printer must be able to print at such layer heights. Any FDM (Fused deposition modeling
) or FFF (fused filament fabrication) printer, which is the type you describe in the question, is able to print at 0.1 to 0.3 mm with at least a 0.4 mm nozzle diameter.
There is also notion of optimal layer heights. Optimal hight depend on full steps of Z motor correlated with a leadscrew type. It is especially important when microstepping for Z is disabled or when printer disconnects a Z motor during long printing of single layer, otherwise positioning may get imprecise. Prusa calculator helps to determine these values. For 8 mm/revolution lead of screw (standard T8 in Ender 3) the step for optimal heights would be 0.04 mm.