how to sort people

You would have to recreate the People album manually with smart albums.

• Create a folder "Sorted People album"
• Open this folder in the sidebar
• For each named person create a smart album: File > New Smart album and name it like the person
• Set the rule of the smart album to "Person is ..." and select the name of the person
• Now you can sort your own People album by ctrl-clicking the folder and selecting "Sort by Name"
• You can structure your on people album by creating subfolders for each family or related groups of people.

For example, just a few named statues and animals:

It will not work however, if you need to sort thousands of people, because Photos may be very slow , if you create too many smart albums.

In latest versions of MacOS, only by dragging them into order.

I wrote a new user tip to describe the method with the smart albums: How to create a custom People album that can be sorted - Apple Community