I did the same thing even on my PS5. Saved the file like normal which saved to the cloud, then i disabled cloud saving and proceeded to do everything else off that save to get each ending and then copy that cloud save back down overriding my local save. I was shocked it worked so well. I think i ran into 1 issue with getting all the weapons since 1 could not be obtained again in the first play through but i had my friend join my game and he gave me the weapon and laughed when we realized it worked. I love that i not only beat that game but also got every achievement, so i guess that means i do enjoy them.