JXA script (JavaScript AppleScript) to set Photos.app titles ("names") from filenames, but changing the first letter to uppercase.

example.jxa

var Photos = Application("Photos")
var currentSelection = Photos.selection()

for (var item of currentSelection) {
	const oldFilename = item.filename()
	const newFilename = oldFilename.charAt(0).toUpperCase() + oldFilename.slice(1)
	item.name = newFilename
}