Does enabling in-game music affect lag?

Muting music in Growtopia shouldn't really affect lag, since the code for the music settings is made this way: You can turn the volume to any number between 0% and 100%, but that only determines how loud the music is. The music is always playing in the background, even if the volume is set to 0%.The same thing applies to SFX.

If you want to avoid lag, though, I suggest turning the graphic detail option all the way down. That will affect lag since it's simplifying the code for rendering the background and other graphic aspects of the game, resulting in smoother gameplay.

Concerning the following comment, "I realised that when I disable the music volume and sfx volume, my game become smooth", correlation does not mean causality, that means the lag had to be affected by some other aspect.

In conclusion, no, turning the volume for everything down does not affect the lag.