Batch change photo titles with sequential numbers in Photo app. Need updated step by step instructions

There are some scripts available that work well:

Thematic Index to Photos for Mac related … - Apple Community

Personally, I use the app Photos Workbench ($30) which gives all sorts of flexibility with titles, like this:

Here, "Counter" increments a number in the Title. You can put an albums pictures in a custom order, independent of dates or filenames, and the counter follows your sorting.

This menu lists some of the options you can include in the Title:

I also like that Photos Workbench offers Search & Replace for a batch of titles, so I can fix my mistakes.

This Apple Script will do what you want: Batch Change Title to Text w/Padded Sequential Numbers. Then do the following:

1 - Copy the script and paste into a Script Editor window.

2 - Compile the script and save as an application.

3 - Place the app on the Desktop or in the Dock.

4 - select the photos you want to rename (they should be in the order you want) and launch the app.

It'l look like this: