You can sort Folders and Field entries either alphabetically or in a custom order of your choice, if you're an admin.

To change the sort order between alphabetical or custom, go to Admin > Folders > "Ordering":

If you have chosen alphabetically but change your mind and would like to return to custom ordering, just choose that option and the order of the items will be restored to how it was prior to making it alphabetical.

Can I have a different sort order for one set of folders compared to another, e.g. sub-folders vs parent folders?
No, currently the ordering applies to all folders at the same time.

If you'd like to order one set of folders alphabetically, and another set of folders in a custom order, you can use the following workaround:
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1. Set your ordering to "A-Z"

2. For the folders you want to apply a custom order to, add "A", "B", "C" etc (or numbers) in front of the folder names, based on the order in which you want them to appear:
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So now, the sub-folders under "Wedding photographers" have been sorted alphabetically, and your parent folders are sorted in the order you want them, by putting "A, B, C, D" in front of them.