How can I copy a photo album while keeping order on MacBook Pro?

léonie wrote: … Then drag the Photos Library from the Pictures folder on your Mac to the flash drive. This will create an exact copy of your Photos Library on the Flash drive. Just double click this copy to open it in Photos.

Just a word of caution-- the Flash Drive would have to be re-formatted as either APFS format or Mac OS Extended (Journaled) format to avoid damaging the Library. There have been so many problems with using incompatible drives that the newest macOSs won't even allow a Library on a non-Mac formatted drive to open, since there is a chance of damaging the Photos database. See this:

Move your Photos library to save space on your Mac - Apple Support

Most flash drives are pretty slow, so I'm not sure you could really operate a substantial Photos Library from a Flash drive at all. There are some flash-looking drives that are fast, but they're not cheap.

You can put a Photos Library on a Flash drive, even one formatted as ExFat, for transferring, but you shouldn't try to use it from a non-Mac format.

This is about sorting. Sorting is the order in which items are displayed. In a Photos album you can drag the items into any order you wish. However that facility doesn't exist in the Finder (which is what manages your flash drive).

To do what you want you need to export from Photos to the flash drive, and to preserve the desired order you can choose a simple sequential naming pattern, and this will then sort in your preferred manner on the drive. It's an option in the Export dialogue in Photos:

File -> Export

If you need to to this again outside of the library here's another way to more definitively title the photos with padded sequential nos on the end of the file name:

1 - use this Apple Script to re-Title the previously sorted photos: Batch Change Title to Text w/Padded Sequential No. - Apple Community

2 - exert the files using the Title as the new File name.

It'll work like this:

As Yer_Man says, plus pictures:

Select all the pictures in an album and use Use File>Export>Export nn Photos and choose Sequential:

You choose a name for the set, and then you get this:

By the way, notice all the choices in "Export." If you use Drag & Drop, you don't know what you'll get-- will it be the same as the last choices you made? Will it be a preview sized file? Will in include metadata? You can see why we don't use Drag & Drop or Copy & Paste when we care about what we'll get.

Do you want to create a second photos library, identical to your current library?

Then drag the Photos Library from the Pictures folder on your Mac to the flash drive. This will create an exact copy of your Photos Library on the Flash drive.

Just double click this copy to open it in Photos. The albums in this library should be sorted exactly as in the original library.