Notice the differences between Rev. 5:9 and Rev. 14:3

 

In Rev. 5:9, they sang a new song.  The “they” are the four beast and 24 elders who are singing a new song.

 

In Rev. 14:3,  they sang as it were a new song, which implies it was not a new song but only a new song to them.  Also, no one could learn that song except for the 144,000 and they were singing it to the 4 beast and 24 elders.