Photos in Ventura

You can use this AppleScript to batch change the Title (if empty) to the file name with or without the extension:

Script: Changing the Title to the Filename without Extension

Script: Batch Changing the Titles to the Filenames with Extension

If you have some titles already in the Title field you can batch clear them out with this AppleScript:

Script: Batch clear the Title of selected items - Apple Community

Also what view are you using to look at your photos? This screenshot describes how the different views in a Photos library can sort the photos:

Copy the code from the site and paste it into a Script Editor window. Click on compile button and save as an application. Then select the photos you want to add the file name to the title and double click on the app you saved.

Is 1 .JPeg in fact the title of your picture, or is it the filename. Photos does not sort by filename. Filename can not be changed, but title fields are originally blank, and if you want a title, you must enter it into the title field at the top of the info window.

The title appears dark with the thumbnail. If there is no title, then the filename appears with the thumbnail, but it is gray.

Is 1.JPeg entered as a title, or as the filename?

I'm sorry-- I'm still not sure I get it. In the Info Window there is not "name" field. What do you see in the Title field and what's in the Filename field, like this:

In this Info Window, there is no title, so the filename is used below the thumbnail.

Sort by title is not available in any of the pre-set Apple views like the Library view or Recents.

I use Photos Workbench ($30) to change titles. It has options like this:

or this:

with choices like this:

Easy and intuitive. I've been using this for quite a while, and it's from a reputable and responsive company.

You are showing the Info window from Finder (which doesn't show 1.JPEG at all.) This appears when you select a file in Finder. But if you are in the Photos app, the place where "sort by title" comes up, then you can select a thumbnail or expanded image and in the menu select Window>Info to pull up the window that I used above. That is where titles can be entered.