If your search intent is Create Fabric 1.21 1, make the 1.21.1 game profile the starting point. Avoid mixing a 1.21.1 installation with files left over from 1.20.x or another branch.
Create a clean 1.21.1 profile
A dedicated profile helps you see whether the base setup works before other mods complicate the diagnosis. Give the instance a clear name and keep its mods and config folders separate.
Check required dependencies
Read the requirements associated with the release you choose. A dependency message after launch usually means a required supporting mod is missing or the installed version does not satisfy the release.
Use a short validation sequence
- Launch the Fabric profile once.
- Add the required dependencies.
- Add the version-matched Create file.
- Launch to the title screen.
- Create a fresh test world.
Keep migration separate from installation
Do not upgrade a long-running world in the same moment that you are also changing loader, dependencies and the main mod. First prove the new 1.21.1 profile works on its own, then copy a backup of the world for migration testing.
Next steps
After confirming your target version, continue with the Download, or browse the full guide library for more setup checks.