As of iOS 18.4 and iPadOS 18.4, there’s Memory Movie support in the Photos app for custom slideshows, and new emoji characters. To use it:
° Launch Photos.
° Scroll down to Memories: and tap “Create A Memory Movie.”
° Type a description: of the movie you want to create.
° Tap “Done.”
Now just swipe left: to see the memory movie you created.