The curve is not good. Why is that?

If you rotate the art 90 degrees in LightBurn and resend the job does the behavior move?
There are a few things that can cause this.
Did you draw these using arc and circle drawing tools in LightBurn or are these files from a vendor.
The right leg of the mouse has a finer sawtooth shape than the pillow. This leads me to believe that it is not exclusively in the belt drive system or exclusively machine harmonics/vibration.
Short line segments may be starting and stopping the engraver, causing this behavior.

• Andrej

  : Sorry for the delay. I lowered the speed to 12 mm/second and got much better results. It seems my Chinese laser cannot cut well with 20+ mm/second. It’s a pity to cut 4mm plywood at 12mm speed