Hey Guys ^^,
I am using the current version 32.0.38 for Minecraft 1.16.1. I know its just a unstable build but i think,
i have found a bug were you can't create a new world with data packs added through the new button in the world creation screen.
after some search in the big open world wide webs i didn't found something related to this topic maybe because its such a new version of forge.
Creating a world without just works fine.
I've created a GIF for visualization purpose.
hope this helps by squishing the bug.
Stay Healthy
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