No offense, but I don’t get it.
One could safeguard thousands of movies, song, art of any kind, that might disappear because some of it becomes lost media. Instead some prefer to backup content made for an ad platform.
I genuinely want to know what these 1m are about
Using the website or connecting to your iCloud account on each phone. Photos app will do it
You don’t. Once they are all on iCloud you can use their smart storage option where it only keeps some locally. I then download them all from iCloud using icloudpd
It’s built in the photos app …
Upload all to iCloud, use the built in duplicate manager (doable directly on your iPhone in the photos app).
It will look at more than just the file name…
Then do a clean backup using icloudpd which will neatly file them by year, month and day
wtf that’s the price of 8TB in Germany