What does "Waiting for changes to be applied" mean?

I usually use ICloud to sync my Mac iTunes (12.8.150) running on Sierra to my IPhone 8Plus running IOS 11.

But occasionally I like to manually back up my IPhone to my Mac iTunes to be safe. In July 2018 I did an encrypted complete backup to my computer.

I was just backing up IPhone connected to my Mac iTunes...it asked to sync new IPhone purchases which I said yes. Then it asked for something else and I hit the button. But for the last hour got a reading that said "Waiting for changes to be applied." Didn't do anything although a round arrow circle was turning for the last hour or so. I was NOT making a completely new manual backup to my Mac...just a sync update. I just stopped it and pulled my IPhone out. But I don't know if I seriously broke anything either with my Mac iTunes and my IPhone.

What does "Waiting for changes to be applied" mean on my Mac iTunes when my IPhone was connected and why did it just keep going for over an hour without seemingly doing anything? And did I do anything serious to my IPhone or Mac?

I restarted my Mac and rebooted my IPhone. My IPhone music said the music was just on my IPhone so I don't know what that means.

Any help you can give me will be appreciated. And yes...I plan to upgrade...one of the reasons I wanted to sync my iTunes up to my IPhone.

Please help, I'm very worried I lost something.