I don't know how but someone noticed me that my music just got allowed in Geometry Dash suddenly. I'm very surprised! If I'm wrong, please go ahead and try to search an ID of my latest song, for example.
So yeah, after 4 years my music is now avaible in the game, I suppose now you all can make levels with them.
Just want to clarify, I didn't make music specifically for GD levels, my songs were originally thought just for listening. But of course you can use whatever track you want.