Can I fix this Geometry Dash bug?(Move Speed)

What you are experiencing is not a bug and can be easily fixed. Go to the Options and disable 'Smooth Fix' (if you are playing the Steam version, it should be under 'Advanced Video Options').

This setting slows down the game instead of dropping framerate. I personally also like disabling it and playing with lower framerate, since Smooth Fix adds inconsistency to timing and offsets the soundtrack.