Why are my albums in Pictures not uploading to iCloud?

richardfrombordon wrote: …The Pictures app I am using is not on the SSD but on my iMac hard drive.

We don't know what you're meaning. There is no "Pictures" app made by Apple. The Photos App is located in the Applications folder, and the Photos Library is in the Pictures folder.

I have set this as the System Photo Library, I have turned on the iCloud Photos and selected Download Originals to this Mac. However there is no sign of any syncing or uploading yet.

Are you absolutely sure that the Apple account you are using on your Mac is the same one you're checking at iCloud.com? What do you see at iCloud.com?

The utilities folder is still showing my imported images as "Unable to upload". I am going to restart my iMac to see if that helps, and I'll do some 'housekeeping' too. I'll let you know if that works.

The only time I had "Unable to upload" show up in Photos, I re-built my Library, and that seemed to fix it. You are working with the library on your Mac, right? And you have a copy of that on the SSD, is that right? Then you should try rebuilding the Library. Close Photos and re-launch by option-command-clicking the app icon. If you use iCloud Photos, it’s possible that this will cause a re-sync that lasts long enough to make you nervous. For me, though, it was fine.

More vocabulary: iCloud Photos is different from iCloud Drive. iCloud Drive is a folder on a device for which all the files in it are copied to iCloud Drive at iCloud.com. iCloud Photos is for pictures controlled by the Photos app to be copied to Photos at iCloud.com. So iCloud Photos and iCloud Drive are two different sections (among others ) at iCloud.com.

iCloud Drive is for files like .doc, .pdf, etc, and iCloud Photos is for pictures like .jpg, .heic, etc.

As Yer_Man said, if your SSD is not formatted as APFS (or Mac OS X Extended, Journaled) then stop running Photos with it immediately!  A Photos Library can sit on an incompatible drive, but running it may corrupt the database.

“iCloud Photos has been turned off" means you are not connected to iCloud. If your drive is properly formatted, then (rather than clicking on Photos) double click on the Photos Library in that drive, verify that it shows the pictures you expect, and go to Photos' Settings>General and see if you are using the System Library:

If "Use this as the System Photos Library" is not grayed out, then click on it to make this your System Library. Only the System Library can connect to iCloud. Then go to Photos' Settings>iCloud

And turn on iCloud Photos.

Then syncing should begin. Let us know.

I'm not sure what you mean by "backed up my iCloud photos to an external SSD." What did you actually do? Did you use Time Machine? Did you copy your Photos Library.photoslibrary to the drive? Did you download images from iCloud.com, or did you download originals from there? Can you be specific?

I'm also not sure what "deleted the content of Pictures on my iMac." means. Did you delete everything in the Pictures folder on your Mac?

I get that you find iCloud confusing, and you're hardly the only one. Are you syncing iCloud Photos, or iCloud Drive or what? And have you turned on "Optimize Storage" on your devices? Including your Mac?

We may be able to help, but we need to know what you actually did.

( I'm not sure I need to say all of the following, and you didn't ask for this-- please ignore as necessary…)

Except for the mobile backups, iCloud is not meant as a backup service. The reason we use iCloud Photos and iCloud Drive is so that this makes our stuff available on all of our devices. 

iCloud Photos is a synchronization service. When you engage iCloud Photos on a device, then the Library on that device is kept exactly the same as the iCloud Photos Library. So, for instance, if you take a picture with your iPhone, it is added to the iPhone's Photos Library, copied to iCloud Photos Library, and then copied to the Photos Library on each of the other devices that you have connected. If you delete a picture on your Mac, then that picture is deleted at iCloud and on all the other devices. 

So you can't think of iCloud Photos as a backup service, since it backs up mistakes, and there's no way to undo them. Whatever you do with Photos on your device-- it happens everywhere else.

Another use of iCloud is Optimize Storage. You can set this on any device, independent of the others.  If you set a device to "Optimize Storage," then Photos may store only smaller images on the device and rely on iCloud to keep the full sized images. Having screen-sized images stored locally allows you to quickly scan through you pictures while saving lots of storage space. And, if Optimize is chosen, and you want to Edit a picture, Photos will reach out to iCloud to get a full sized image for you to work on. Your optimized Library may take up less than 20% of the space of a fully downloaded Library. But an optimized Library may be kept larger than that if the extra storage space is not needed.

Beware, though: backing up a Mac Photos Library with Optimize Storage only backs up smaller images. If you want to keep a true backup on an external disk for safe keeping, you need to have Download Originals checked. I use Optimize on my phone, but not on my Mac.

If you need something other than synchronization and optimizes storage, then iCloud may not be for you. The only things I sync with iCloud are things I also want to see on my Mac, phone, and iPad.

iCloud Drive is similar, but for files, and Optimize works a bit differently. See this:

Understanding iCloud Drive - Apple Community

I then opened the Pictures App (why isn’t this called iPhotos?)

There is no such thing as a "Pictures app". Not was there ever an app called iPhotos, but there was one called iPhoto. The current app is called Photos. Not that any of this is remotely confusing, of course. But clarity...

What format is the external SSD. It needs to be formatted Mac OS X Extended, Journaled or apfs.

richardfrombordon wrote: …At the top of the iCloud Photos browser is the message "Cloud Photos has been disabled.You have 26 days remaining to make sure you have a complete copy of your photos and videos"

When iCloud is turned off, syncing stops and the stuff at iCloud.com hangs on for 30 days. Clearly, this iCloud account thinks that you are not connected to it. Have you indeed verified that the accounts are the same? Is it the same email address?

How's the weather there? It's clear and 35°C in Texas.

By the way, I think you should go to iCloud.com and, at the bottom, check "Your Plan."

Well, that's cool! I hope our discussions were useful…