how can i rephrase this so that both parts are parallel Lots of my friends think that Prince's music is old, but I think it's not only excellent but also an innovation.

You have two adjectives modifying "Prince's music" -- old and excellent. But that third one ("innovation") needs to be an adjective, too, not a noun.

Lots of my friends think that Prince's music is old, but I not only think it is excellent, it is also an innovation.

To rephrase the sentence so that both parts are parallel, you can use similar sentence structure and phrasing. Here's a possible rephrasing:

While many of my friends consider Prince's music to be old, I believe it is not only excellent but also innovative.

In this rephrased sentence, the structure "While [many of my friends] [consider...], I [believe...]" makes both parts parallel. Additionally, "not only excellent but also innovative" maintains parallelism by using the same conjunction ("but also") to connect two adjectives that describe Prince's music.