Lightroom is an absolute HORROR to use. If the free features are anything to go by, signing up is the-worst-idea-ever.
1. Lightroom can't import photos in the same order that they're picked in Files if life depended on it, no matter what you do.
a) Create a new album and sort the still empty album by 'Custom'.
b) Start adding photos from Files, one at a time. It doesn't take long before they start to line up in random order. Adding just one single photo doesn't matter, at any time it can end up anywhere in the album.
c) Try adding a bunch of photos all at once from Files. Now and then, and sometimes repeatedly, they end up in scrambled order in the album no matter how they're sorted in Files, and no matter if they're selected in Files by 'Select all' or one by one, before opening all of the selected photos.
d) Try a couple of times deleting all photos in the album and then import all of them again from Files and you're sure to run into trouble.
2. Sorting the photos in the album by 'Custom' and drag-and-drop is a joke.
a) More often than not it just creates a mess, photos that aren't supposed to move at all just moves around like crazy. And when you switch the first and second photo, or the last and second last, you risk ending up with all photos suddenly lining up in reverse order(!).
b) When you have many photos in the album, you can't drag photos past the first or last photo in view. Also, sooner or later you'll find that you can't scroll down to the last row of photos: you can't get those photos in full view at all, only a thin slice of the upper part.
I'm sure I won't have any trouble at all finding more problems but I've had enough. I'm removing this abomination of an app from my iPhone.