I took 7 new photos on the iPhone. The phone then after a few minutes said "7 of 7 uploaded".
I'm not sure what you mean by "just means it has uploaded all items it can upload, not necessarily, all items from the library". Why wouldn't those be the same thing? I have plenty of iCloud storage, and the iPhone was on a working wifi network with internet access the entire time, as was the laptop.
I've been on MacOS 11 for a very long time now and have used iCloud photos back and forth many times before this issue started happening. I do not think incompatible files are the issue here. There was also no indication from Photos on macOS that any items were pending: it simply said it last updated about 8 hours before. I just ended up airdropping the photos so I could use them since iCloud/Photos wasn't working.
My question is: if all indications are that the photos have been successfully uploaded to iCloud, how can I tell Photos on macOS to check for new photos and download them? There should be some sort of sync button or something, but that might make too much sense for Apple.