UPDATE: I think I've found how to do this:
1) If you are going to shoot, or already have shot, a lot of photos or big videos on your iPhone or iPad, turn off iCloud Photo sync on the device. (note: This did work with my iPhone 7 Plus, video to iMac, even though I never turned off iCloud Photo sync on the iPhone.)
2) After finishing the shots, connect your iDevice to your Mac via whatever cable you use. Trust the computer and enter your Mac password in the pop-up.
3) Open the Photos app on the Mac, NOT Finder!
4) In the Photos app, on the left-hand side for me, there will be a new device listed, your iPhone/iPad. Click that.
5) Select the photos/videos you want to transfer. (You might need to click "Show all" on the right and scroll around to find your videos/photos.)
6) At the top center, change the" Import to" to a diff/new album if you wish, then click Import ("Delete after import" option is also there, but I'd wait and delete manually after you've made a second backup somewhere), and the files will go to your Mac over the wire and into your Photos app on your Mac.
7) Now this gets confusing. Once you initiate the transfer, you'll be taken to the "Imports" tab on Photos (on the Mac), but you can't see anything from there. Either click the iPhone/iPad device again, and you'll see a "Cancel" button, or click the Recents tab and you'll see the photos/videos when they come across.
8) Use Finder to move the videos/photos out of Photos and into another folder that isn't synchronized with iCloud (just drag them from the Photos app to a Finder window).
9) Make your second local copy of the files.
10) Make sure the files are deleted (and trash emptied?) from the other devices and Photos app before you turn on iCloud sync again, otherwise you'll begin eating up your data allotment and iCloud storage.
Voila! Then you can edit on your Mac and re-upload the finished product when done.
Note: Steps 7 and 8 are not working correctly for me now. On my Mac mini (2018), I could not drag the 24GB video from Photos to a folder in Finder. It crashed Photos several times. Finally I gave up. I hope this is a bug Apple will soon squash.
The whole process is error ridden. Be very careful. As it is now, you could easily lose a video during the transfer. Never have just one copy once you've made the first transfer.
You could also end up flooding your network if one of your devices is trying to upload these giant media files in the background. I repeatedly found deleted photos and videos were not being deleted on all my connected devices during this procedure. I think something is wrong with iCloud now causing this, though. A lot of my photo edits made a month ago were lost last week when Catalina came out.
For now, transferring files via AirDrop is a more manageable, reliable, though slower process.
Transfer speeds:
AirDrop: one-hour long, 25GB video in 30 minutes (1GB/minute).
iPhone 11 to iMac via USB-Lightning: 2 minute long, 1GB (?) video in 33 seconds (2GB/minute)
note: a five minute long, 2.5GB(?) video failed to transfer 3 times over USB-Lightning, and I gave up trying.
iPad Pro 11 to Mac mini via USB-C/Thunderbolt:
2min, 1GB(?) video transferred in 6 seconds (10GB/minute)
5min, 2.5GB(?) video transferred in 15 seconds (10GB/minute)
1hour, 25GB(?) video transferred in 1minute 33 seconds! (15GB/minute)
Edit: Once I've shot the video/mass of photos, I'm still of a mind to copy them to Files on the iPad, and then from there to my USB/Thunderbolt 3 SSD (1TB G-Drive), but:
1) There is no progress indicator during the copy (there's just a spinning "flower-petals" icon).
2) It crashes, crashes, crashes... ( The operation couldn't be completed. Input/output error )
3) There is no USB-C/Thunderbolt on my iPhone. Connecting a USB drive to an iPhone is a whole 'nother challenge.
Edit2: (
https://www.apple.com/uk/shop/questions/product/MK0W2ZM/A/lightning-to-usb-3-camera-adapter ) The Lightning USB 3 adapter allows for the
import of supported files only. If the external hard drive has supported files, it can allow for the import of them. They may have to be in a folder labelled DCIM in order to be detected. Answered by Philip S from Toronto, 28 Feb 2018
Are all of the limitations due to protocols? Or is Apple intentionally limiting device to device transfers even between its own devices?
Edit3: I've just discovered that my iPad 11 backup had swelled from 3GB up to 23GB! The reason: iCloud is backing up everything in the Files "On My iPad", including the Photos.not.iClouid folder I had made. It had 20GB of videos. I looked around and could find no way to exclude directories from this backup.
Apple is making it difficult for me to use my iPad as I see fit. I want to exclude some folders from being backed up. Maybe moving the big items back and fourth between Recently Deleted and Files? Would iCloud include Recently Deleted in the iCloud backup? The workarounds I'm trying to come up with to counter iCloud's aggressive simplicity are becoming more and more ridiculous.
Edit5: I guess I should have seen this. The effect of Apple’s limitations on the transfers results in one obvious solution: carry a Mac! If you carry a Mac with you, then and only then can you quickly and reliably move photos and videos off of iOS/iPadOS devices. (You could also use a Gnarbox 2.0, but one of those “connected smart SSD drives” costs almost as much as the cheapest MacBook. A MacBook and a USB-C drive is the easy way around all these “blocks”.
