There are at least 6 questions, here. Are you not seeing them? If you can't read these questions, you may need to contact Apple Support:
https://getsupport.apple.com
The rest of the questions?
- Do you synchronize your Mac with iCloud Photos?
If so, do you have “Optimize Storage” checked in Photos’ Settings
- Where does your Mac Photos Library reside-- in the Pictures folder of your internal drive, or on an external drive? or on a network? on iCloud drive?
- How is your hdd formatted?
- What else have you tried?
- How many pictures at once? does 1 picture at a time work?
- Suppose you drag the picture to your internal drive, and then try dragging it to iCloud Photos-- what happens?
The questions may not seem relevant, but, really, I asked them to eliminate certain possibilities.