I would like to move the folder Picture to an external drive either
I would like to move my folder "Pictures" to an external drive, and also move the Photos library inn the same device
iMac Pro
first connect the external drive to your mac. then open finder and select the drive in the sidebar.
then open a new finder window.
you will then be able to drag the file(s) from the second window you opened (internal drive on right) to the external drive's window (seen on the left)