When I started to create my new world in the newest snapshot, I accidentally clicked the "Done" button 2 times, and that bugged it, so that it was loading the world and the menu at the same time.

Repro:

1. Create new world
2. Open Datapack experiments and enable a datapack
3. Click done several times rapidly
4. Observe it will start creating the world while it is still validating the datapacks. A distinct second "click" noise is observed when rapidly clicking, indicating the "Create World" button was hit.