1. Open the "Data Packs" selection screen when creating a new world
   
2. Drag the downloaded datapack zip file onto the game window
3. Move data pack to the "Selected" column and click "Done"
   
4. Accept the "Experimental Features Warning"
   
5. Change any other world settings and click "Create New World"
   

1. Select your world and click "Edit"
   
2. Click "Open World Folder"
   
3. Enable the "Update 1.21" feature flag level.dat. A simple way to do this is by installing the NBT Viewer extension for VSCode
   
4. Open the level.dat file in VSCode by dragging the file from the file explorer to the VSCode window
5. Inside Data, add a new list tag called enabled_features
   
6. Inside this list, add two new string tags with minecraft:vanilla and minecraft:update_1_21. Select the yellow string icon when adding the first tag.
   
7. Press Ctrl + S to save the file, make sure the world is not open in-game when editing the file!
8. In the world save folder, find the datapacks folder and put the downloaded zip file in there
   
9. You can now open the world!

1. Download the server jar from the bottom of the 1.20.4 article
2. Place the server.jar file in the server folder
3. Inside this same folder, create the folders world/datapacks/
4. Put the downloaded zip file in there
5. Run the server jar for the first time

java -Xmx1024M -Xms1024M -jar server.jar nogui

6. Agree to the EULA by editing eula.txt
7. Run the server jar again. You should see Found new data pack file/update_1_21_no_trial_chambers_1.20.4.zip, loading it automatically in the log.

1. Shut down the server
2. Modify the world/level.dat file following the same instructions from "Adding to an existing singleplayer world"
3. Add the downloaded zip file to the world/datapacks/ folder
4. Restart the server