back up photos to external drive

Hi,

what you need to do is:

• Manually copy your library to an external storage device: Drag the Photos library (by default in the Pictures folder on your Mac) to your storage device to create a copy.

From here: https://support.apple.com/en-ca/guide/photos/pht6d60d10f/6.0/mac/11.0

Use Carbon Copy Cloner to clone your Photos library to the EHD (it must be formatted APFS or OS X Extended (journaled) and the use CCC to incrementally backup frequently copyping only those modified or new files. This saves copying the entire library each time, very time comsuming.