So I downloaded this file from your subreddit, extracted to the proper directory, saw the preparation screen when mc was loading, and what now? How do I choose the file I dled?

Also, could you please port PersistentChatHistory and BiggerChatHistory to fabric?

The cave animation download only contains the animation. You can set this animation as menu background via the layout editor ^^

There should be good alternatives on Fabric for at least BiggerChatHistory.
I made this mod because nobody made one for Forge, only for Fabric :D
But I will think about porting them.