In the settings for iCloud > Photos, I have checked iCloud Photo Library. This means ALL my photos should be saved to my iCloud space.
Has the upload to iCloud for your Photos Library already finished? Have a look at the Photos > Preferences > iCloud. Is there still a progress bar and does it say "Updated just now"?
And check, if all items in your Photos Library are eligible to upload to iCloud. Your Photos Library might contain items that cannot upload to iCloud.
Check this with a smart album:
File > New Smart album
Add a rule: Photo is unable to upload to iCloud Photo Library.
Is this album empty?
Your iCloud Photo Library should be slightly smaller than the local library on your Mac. The iCloud Photo Library does not store faces thumbnails or previews.
For example. My local Photos Library has a size of 190.69 GB. But in iCloud are only 150.5 GB of photos.