I have an iPhone 14 Pro Max but looking for a third party camera app which automatically stamps the date on photos when taken AND sets 16:9 aspect ratio as default.
You can set the desired screen ratio as default in the camera app, so the images taken with your iPhone show up with a 16:9 ratio in Photos.
In the Camera app, make sure you‘ve selected Photo. Then tap the small arrow at the top:
Go to the aspect ratio (this could also be Square or 4:3):
Select 16:9:
I don‘t know an app that adds the time stamp and allows selecting the aspect ratio as well. There are several apps in the App Store that can add a time stamp to an exisiting image. Just search for “time stamp photos”.