Hard mode - Do I need to finish the chapter?

So I just beat Malboro in shinra battle simulator on hard and got the trophy and enemy skill trophy.

Do I need to now beat all of chapter 17 on hard for the game to save this or can I go to chapter select and go work on other trophies.

I've done battle arena's and left without completing the chapter. I think you only need to complete the chapter for things like dialog choices to take effect. If you're nervous, you could save the game, go to a different chapter, go back to chapter 17 and see if it still honors the progress.

The only thing you need to finish chapters for is decisions that will effect later chapters. For example if you're trying to unlock all Tifa's dresses, you need to finish all the side quests, tell her which dress to use, and then complete the chapter and move on to chapter 4. At which point you can immediately skip ahead to chapter 9 to unlock it.

Anything else like levels, enemy intel, VR progress, materia, skillpoints, etc, are saved whenever you switch chapters.

Awesome! Thanks, I didnt feel like playing the whole chapter now but I gotta grind up some materia to have a chance at Pride and Joy and I want to do a few other things too. (being brutally murdered in the first round against Shiva)

I actually didn't know there was a hard mode, I was very surprised at 'normal' being the top difficulty. I am still only in chapter 3 as my days are irregularly busy for what most of the world is doing by self isolating (I work an 'essential' job), but first of all, I am loving this game to death, so much nostalgia I needed a second helping of that first grossly gorgeous and produced first hour intro/reactor section to soak it in. I fumbled on normal a few times with understanding the active battle system, accidentally hitting the commands and not mapping my toggle commands etc, but yeah, after understanding the combat, I am very happy to hear that there is a hard mode, because I do plan on hanging on to my PS4 for a while, and I certainly plan on re-playing this game down the road the same way I did the original.