Syncing my tracks from my new Macbook Air to my old iPhone 4s deos not complete

I have an old iPhone 4s which I want to use just for music. There is enough memory on the phone but every time I try to do this it sticks on step 6 (waiting to update changes).

I have 2 queries: Firstly how do I disconnect the phone safely and secondly how do I get the syncing to complete

I am trying to sync from my new MacBook Air which uses Big Sur as its operating system and the software on the phone is up to date (iOS 9.3.6)