unfortunately, they removed the option to rename your photos within the gallery app. But as @Dougsteward1 mentioned, you are able to use the Samsung My Files app to rename your photos.
Open the my files app, click on images, and click on the 3 dots in the upper right corner and choose edit. Select the photo you want to rename (can only do 1 photo at a time). On the bottom right corner select More, then Rename.
It's such a round about way to do it. It was much easier to be able to do it within the Gallery app, but until they give us the option to be able to do it within the Gallery app again, this is how you can do it.
So you do not have these options?
You need an additional step in your procedure for most users. Have 2 select the location (e.g. Camera, Camera, Screenshotes, where 1 Camera is SD card and 1 is internal memory), open that to select your photo.