Load old game file after finishing

Hello everyone, This is my first time I'm close to finish the game. I've made myself a checklist because I want to get the 100% achievement. My plan is to ignore NG+ for now because what I saw of it is crazy.

I want to become big to get the 100% but I assume that I cant access the world anymore. My idea was that I finish the game and load a safe file from before. I couldnt find information if that's even possible, unfortunately.

I was hoping someone could answer me that question: Can I go back by reloading after I finished the game to keep my world and begin NG+?

Thank you all ♡ Have an exponentially great day!