Not all photos are uploading to iCloud

First, I assume you're using Photos, not iPhoto. Only Photos can sync to iCloud.

Second, iCloud is NOT a storage or archive space. iCloud is a system to SYNC your stuff between devices. It means whatever file you change on one device will be changed on all other devices. It does store files but it's an active system, reacting automatically to user input on any device. If you're looking for an archiving system there are many options out there.

That said, I would repair the Photos library as a first step. Syncing photos takes a long time but not that long, you're correct.

How to use the Photos Repair Library tool on your Mac - Apple Support (CA)

That repair will take a long time as well, many hours depending on your machine speed and type of drive, HDD or SSD.

Unable to upload will only appear when Photos has identified something that it can't work with.

You could also try a smart album with the condition photo - is unable to upload to icloud.

Also see this article by Leonie about legacy media which can also sometimes cause uploads to stall:

How to Weed out Legacy Media in Photos fo… - Apple Community

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Oh, and regarding the comment above about backup - be aware:

The problem with iCloud for photos (and files if you use iCloud drive) is it makes all the libraries across all the devices the same. While it does protect you from a drive failure - it doesn't protect you from accidental deletion. If you delete photos on your phone, they are deleted on your mac, and from iCloud - same if you delete on your mac - they'll be deleted on your phone. There have been rare cases of system failure also causing deletions (or just user error). There are also numerous examples of library corruption making it very difficult to access photos.

Every few days we get someone here saying "I deleted photos - how can I get them back". If it was more than 30 days ago (or they’ve been manually removed from recently deleted), and there is no other backup, the answer is "you can't"

Always use a proper backup in addition to iCloud.

I have turned the iCloud back up on and off numerous times.

There is your problem. You have a large library that will take some time to sync - easily up to 2-3 weeks based on my experience (My 5000 item 50GB library took a full 48 hours).

EVERY TIME you turn iCloud off and on you restart that sync process from the beginning. So you are never allowing it to complete.

You say you have plenty of iCloud storage - do you also have plenty of Mac Storage?

You are going to need to be patient. Leave the mac on 24/7 with sleep disabled, connected to power and with photos open.

While ongoing, check for an "unable to upload" folder. It is also possible some items that are unable to upload can stall the process. If you have any, export them (unmodified original) to a folder, and remove them from photos (including recently deleted). Once the sync is complete, you can try re-importing them.