New photos in Ventura won't let me title my pictures

The file name can not be changed in Photos, but you can add a title as you like. The title is added in the Info Window (command-I) where it says "Add a Title." This is a separate data field that can be included when you export a picture. You can also add a caption (description) of the picture, and keywords.

Titles could be modified by clicking on the text under the thumbnail, but the text editing was crude, there.

You can also select several pictures and change all their titles at once.

To batch change titles I have been using Photos Workbench (beta 28) from Houdah Software. This is a beta version-- it is free but not finished, yet. It works well with Photos on you System Library.

https://www.houdah.com/photosWorkbench/

I have used it to add dates and index numbers to pre-existing title names, moving parts around for easy sorting, and it has worked very well. Here is an example where I put the date first as 2022 04 01, and then an index, followed by description. They have variables for things like the creation year, current title and so on. Each of the variables can be inserted or deleted independently, as well as text). In then shows an example of a photo title before and after the change so you can see what you've done before doing it.

It's free so far, and they keep adding stuff-- it's worth a look.

What happens, when you try to highlight the title shown below the thumbnail of a photo?

Or is the problem, that the title is no longer shown below the thumbnails for you?

If you are no longer seeing the filenames below the thumbnails, make sure the aspect ratio button is not set to "Square" and in the "View" menu is "Metadata > Titles" enabled.

You're welcome 😊 Great that it is working now.