Is there - Single Choice
Is there any magic mod where it can transport you to a void realm where you cant die but.Create your own universe like planets stars etc with tools if not please tell me if there is please tell me also it needs to be 1.12.2
As far as I know, no there is not, They have mods that let you go into a pocket dimension, put adding planet and stuff like that, it does not.
Okay, so from what I know there is no mod that does what you asked. However, something similar:
Dimensional Doors, allows you to create an Infinite number of your own pocket universes and do whatever you want in them.
link here: https://minecraft.curseforge.com/projects/dimensionaldoors