Knowing how to crop a horizontal image into a vertical one, or vice versa, has been this little secret among Lightroom users for a while now. It’s one of those things that, while it is indeed in a menu, it’s not something that would ever jump out at you. So here’s the secret. When you’re in Crop mode (the keyboard shortcut is R), all you have to do is press the letter X and it’ll switch your crop orientation automatically. If it’s horizontal, it’ll make it vertical. If it’s vertical, it’ll do the opposite. That’s it!
Have a great day!