How do I discontinue photo optimization and download full copies to an external drive?

If all your phtoos and videos are already in iCloud, prepare an external drive as described here: Move your Photos library to save space on your Mac - Apple Support

Then create a new, empty Photos Library on the external drive, see:

Create additional libraries

• Make the new library the System Photos Library in the Photos > Settings > General - click "Use as System Photos Library"
• Make it the iCloud Photos Library in "Photos > Settings > iCloud", and enable to download the originals.

This way you will have a an iCloud Photos Library on the external drive, with the originals all downloaded.

Keep the external volume always connected, before you open Photos.

Karuizawa wrote:

Thanks so much! Very helpful

Will I need to turn off Optimize Mac Storage to download the Photos?

Yes, to download all photos in the full quality to the external drive,you need to disable "Optimize Mac Storage" in the Photos > Settings > iCloud.

After I download the photos onto the external hard drive, is it possible to continue to store the photos on iCloud, so I have remote access to them on my MBP when travelling? or is that asking too much? (The MBP is my only computer and will normally be connected to the new Drive where the photos will be stored)

Your Photos will remain in iCloud, unless you delete them, so your other devices will still be able to access the photos in iCloud.

Only one library at a time can sync on your Mac with iCloud, so you will need the external drive, when you want to work with the Photos.app. If you do not have the external drive with you, you can see your iCloud Photos Library on the iCloud web page at www.icloud.com, when you sign in with your AppleID and launch the Photos.app there.

Karuizawa wrote:

• Thanks again. This is so helpful!

So if I turn off Photos Optimize Mac Storage, download all my full-size Photos/videos from iCloud to my external hard drive

will iCloud still be able to optimize the non-photo files that remain on my MBP?

No, the library on your internal drive on your Mac will be incomplete. You cannot use it any longer, as you can only use one library with iCloud Photos. While the library on the external drive is syncing with iCloud Photos, you cannot enable iCloud Photos on the internal drive. You could switch iCloud Photos back from the external library to the internal library, once the download on the external is complete and keep the library on the external as an archive of all your photos. But it will no longer sync with iCloud, if you switch iCloud back to the Internal.

• is there any advantage to just moving all my documents to the external hard drive? I've never used an external hard drive for my documents

An external drive is fine for any kind of documents and media files, that are large, if you are running out of storage on the internal drive. If you do not want to keep the external drive connected at all times, move only items to the external drive, that you do not need at all times.

Or get yourself two very small portable external drives, that you can easily carry around with mac. You will need the second drive to make backup copies of the data on the first external drive. To able to restore your data, if the drive should fail (every drive will fail one day) you need a safety copy of the documents and data.