Cookie_roll12

Note: I am new to modding for Minecraft. I am trying to recreate a time travel dimension, I guessed it uses custom dimensions so that's why it is about dimensions. The effect I am trying to achieve Now I made two dimensions, Past far and past. Now past is like the overworld, and Past far is a stone/rock-like version of the past. But past is not like the overworld in any way. how can I achieve this? Also, I have looked on google on how to do this but there is only one post and that is about version 1.7.10. I am not sure but since 1.16.5 I think you have to use JSON files. Thanks.