Limit # of photos shared to icloud photos -- is it possible?

iCloud Photos is all or nothing. However on a Mac you can have multiple Photo Libraries and only the System Photo Library is synced with iCloud. See: Designate a System Photo Library in Photos - Apple Support

It is all or nothing. The purpose of iCloud Photos is for syncing the same photos across all devices so one device will look exactly like the other. It has never been intended to be used as a storage service like the Files app. If that is not the service you are interested in, then I would suggest not using it.

If you just have a few photos that you would like to view on another device or save to the cloud, then you can save them in your Files app. The advantage of using iCloud Photos is that the storage on your device is automatically managed using the Optimized Storage option so your device does not use storage for the full resolution photo.

JSmith_MD wrote:

Am I missing something?

Nope. Not missing anything,.

Or is this service really all or nothing? (I'll stick with nothing if that's the case.)

iCloud Photo Library syncs all your photos on the device, as long as there is space for them. There is no option to limit them.

There is a fine distinction. On a Mac iCloud Photos is syncing all photos from the system Photos Library and ignores all additional Photos Library. We are not forced to keep all our photos in our System photos library.

Keep the system Photos Library small enough to to serve jus as a replacement for My Photos Stream with just the new photos and your most important favorites, and remove all other photos to an additional archive library.

léonie wrote:

There is a fine distinction. On a Mac iCloud Photos is syncing all photos from the system Photos Library and ignores all additional Photos Library. We are not forced to keep all our photos in our System photos library.

Keep the system Photos Library small enough to to serve jus as a replacement for My Photos Stream with just the new photos and your most important favorites, and remove all other photos to an additional archive library.

This is true. A bit convoluted, but yes, this is an option on a Mac, not so much on an iPhone or iPad.