Final Fantasy 7 Rebirth New Game Plus (aka Hard Difficulty) explained

Your first playthrough of Final Fantasy 7 Rebirth will take you anywhere from 30 to 100 hours, depending on how much of the world you explore and how much of the side content you complete. After beating the main storyline, you may be tempted to continue your playthrough.

Many open world RPGs offer the ability to restart your journey through New Game Plus. Oftentimes, all of the content resets and you play through the game all over again from the beginning but with all of your equipment, levels and skills carrying over.

Final Fantasy 7 Rebirth doesn't have a traditional New Game Plus, but still offers a way to continue your playthrough.

When you beat the game, you'll make a new save file that will don a teal tag that says "Chapter Selection" when you view the file. This file will allow you to continue to replay chapters of the game with the current characters' levels, weapons, material, and relationship status, or play it on Hard difficulty. Whatever chapter you select will carry over all of your data from your completed run save.

If you're chasing the Platinum trophy, you'll need to complete every chapter on Hard difficulty.

The first time you go to Chapter Selection, you'll be greeted with the following prompt:

Replaying a portion of the game via Chapter Selection will return you to the start of the chosen chapter. Your current characters' levels, weapons, materia, and relationship status will carry over. 

You can also choose how to carry over your quest data. Note that any odd jobs you have yet to complete will automatically reset. 

When you select a chapter, you will be given the option to play it on Hard difficulty. Be warned that you cannot change this setting once you begin the chapter.

Even after beating the game, you can continue to improve your character. All progress your characters earn during your chapter playthrough will accumulate and carry forward to the next. For example, if you replay Chapter 5, any additional levels and items you earn will upon completion will be brought with you to the next chapter you decide to play. So if you start Chapter 6, all of the new levels you earned from Chapter 5 will carry over.