I have a question on this category which difficultie can be used. Its not explained if it must be on hard,normal or safety.

In this case anyone can just run on safety for the easiest progress at all right?

I am not one of the mods, but I have speedrun the game on safety and hard. There is very little difference in time lost if you have your demons set up correctly. In fact there is already a sub 2hr speedrun of the game on hard from a modded save with 999 stats. Since theoretically someone could hunt for stat increasing items until they hit the cap, the difficulty doesn't really matter as you can eventually be in a position to one shot all enemies, even the bosses.

allright thank you for the information. I thought there are some differences in how fast you run it in which difficulty. But it theoraticly its right if someone farms the stat ups you can make it in any difficulty without any problems.