I’m no expert on this myself, but from what I’ve been reading you are likely looking at modifying the engine side of unreal to achieve what you’re looking for.
Doing a quick search in the UE5 source (my local build, so may not be 100% up to date, you may want to do the search yourself just to be sure) came up with nothing for UIImageWriteToSavedPhotosAlbum. Which is what I could find in the iOS API for saving an image to the device’s photo album.
Again I’m no expert here, but this seems like something you’d need to add manually yourself.
You may also be able to look at Building UE As A Library and writing a lightweight Swift app to wrap your game - where you would have more access to the iOS API.
Finally I found this thread which didn’t seem to come to a solution, but might have some good jumping off points if you’re ready to delve deeper into the engine