Removing previously synced photos/videos from iPhone

After getting my iPhone 13, I synced my iPhone 7's photo library with my iMac's and then synced that library on to the new iPhone 13. I now wish to remove those synced photos and have had only partial success.

I connected my iPhone 13 to the iMac and unchecked Sync photos to your device from: Photos in finder, where I was then asked if I wanted to remove all previously synced photos from my iPhone. I confirmed I did and clicked Sync. The process completed with most photos being removed, but I still have hundreds of photos in my library that should have been removed as well. Furthermore, the Photos app now permanently says Syncing... at the bottom of my library despite disconnecting my phone, closing the app, and restarting the iPhone.