Copy live photos and all meta data to external device

You mention iPhoto, but it must be a typo. iPhoto has no longer be supported since 2015, before the Live Photos have been introduced. You need to use Photos for Mac to be able to see Live Photos animated. Which system version do you have installed on the Mac? Is macOS 11 Big Sur installed?

Then you can save the Live Photos with any Live Effect applied by exporting them as an animated GIF. An animated GIF can be used on other platforms as well. You should be able to see it animated on Linux or Windows. The only problem is, that the GIFs will be huge and increase your storage problem. I just tested by exporting a Live Photo with the Bounce effect applied - the original has a size of just 220 KB, but the exported animated gif has a whopping 19MB. Another Live Photo with 3.1 MB resulted in a GIF of 22MB.

A Live Photo is stored in Photos as a collection of two or more files: A high resolution still frame of the key photo (a JPEG or HEIC file), a short video clip of the animation (a MOV or mp4 file), and optionally an .AAE sidecar file with adjustments. When you export a Live Photo with File > Export > Export unmodified original and enable "Export IPTC as XPM", you will get a sidecar file with the metadata as well.

I have archived my Live Photos by exporting them this way. When I reimport the Live Photos into another Photos Library, by importing all four files together, the Live Photo will play again and can be used as a Live Photo. On other platforms you can probably view at least the still frame as a high quality photo or play the video to see the animation.

Hi

If he is using the photos app, the best way is simply to move the entire library to external storage with the disadvantage that you must have the external storage connected whenever you log onto your machine. It can still sync with iCloud (if you use that) by setting it to the system library after the move. The drive needs to be properly formatted as described:

(You cannot use the synolgoy NAS if you want to use the photos app - and if you have a referenced library (Image files not stored in the library) you probably need to change that and consolidate the files into the library first)

It must be formatted APFS or MacOS extended (journaled) (preferred for spinning drives)

It Must not be (or have been) used for time machine. (A time machine drive can be used if re-formatted)

It must have the 'ignore ownership" checkbox ticked.

It should not be on a memory stick, SD or similar.

It stands to reason that if you want any sort of reasonable performance it should be a fast drive with a fast connection.

It must also not be a network drive (a direct connection is required - eg USB or Thunderbolt). File sharing services such as iCloud Drive, Drop box, Onedrive etc are not compatible with Photos libraries.

See

https://support.apple.com/en-gb/HT201517