Can't Upload Photos to Shared Album

See this article How Photos and iCloud Photo Library handle RAW images - Apple Support

RAW files that you store outside the Photos app library (for example, in your Pictures folder) are always present on your Mac, but aren't stored in iCloud and won't stay up to date in the Photos app on your iPhone, iPad, or iPod touch.

The message may be given, if you cannot download a larger version of the photo for other reasons, for example, if you are running out of storage on your Mac or in iCloud. How is your storage situation in iCloud and on the drive with your Photos Library?

Are you still signed into iCloud with your Apple ID?

Thank you! that article is super helpful. They are RAW photos taken with a Nikon DSLR, and they have made their way into iCloud photo library (I can see them on all my devices).

But can your Mac (where you want to share them) edit the files? If not, check, if Photos is really using the library on your external drive. Photos is showing the location of the currently open library in the Photos Preferences panel: Photos > Preferences > General: Library Location

Is Photos really currently using the library on your large external drive or did dit open a library on your system drive?

See this article My Photo Stream and iCloud Photo Sharing limits - Apple Support

are you using a VPN, firewall software, ilttle Snitch, or other software that can interfere with internet service for an application?

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