I recently in my photos app and the upload is going extremely slowly, as in less than 100 photos per day.
MacBook Pro (Retina, 13-inch, Mid 2014) running Big Sur, 11.7.2 - I just checked for updates, and looks like I’m a bit behind, with 11.7.6 available. Will update and report back if things improve.
In the meantime, photos tells me I have 36,296 photos, and on April 20, it reported uploading 33,822. This makes sense, since my iPhone is already in iCloud, and I sync my iPhone to the computer.
Today is a couple weeks, and photos is now reporting 32,499 uploaded. So a whopping 1,323 uploaded!
I have a few thousand fewer photos than you in my library. I recall when I first turned on iCloud Photo Library it took days to sort out, not weeks. I was probably on Big Sur at the time but am not completely sure. I can’t recall how many days it took, but it was quite a while. But it averaged several thousand a day, not a hundred.
You might want to prevent system sleep–I recall that seemed to help. Also experiment with whether Photos is open or not overnight and whether it’s in the foreground. If I remember it right it’s non-intuitive–it might be faster letting the agent run while Photos is closed.