Such items can block the upload to iCloud and prevent new photos from being downloaded. You may want to check if your library contains items that are no longer compatible with Photos after the upgrade to macOS 11. Your Mac will start downloading new photos from iCloud Photos, only once it has finished uploading all local photos from your Mac to iCloud. If your iPhone has finished uploading, it just means it has uploaded all items it can upload, not necessarily, all items from the library.
To repeat Tony's question - have you checked, if the iPhone photos are already in iCloud? You can check this by looking at your iCloud Photos Library at Are the photos already in iCloud? This will tell you, if the iPhone is the problem or your Mac.