After moving System Photos Library to External Drive - can I Download Originals?

Hi All,

I have a large photos library ~2TB, 100k+ photos, that is optimized on my current HD as it is too large.

I saw a solution of moving (i.e. copying the Photos Library) to an external connected drive (https://support.apple.com/en-hk/HT201517).

I want to understand if after that, it is possible to Download Originals onto the external drive so that I can make proper backups?

Best,

Andy