Before Continuing:

• Check you are using the latest version of the mods and its dependencies
• Always include a latest.log if you are crashing
• Remove mod that enhances Minecraft: Optifine, Sodium, others. The issue persists.
• If you are unsure which mod is the culprit.
  Disable all of your mods and enable them 1-2 mods each time to isolate the culprit
• Confirm that there is no existing issue with a similar description submitted in the list of issues.

Version

1.21.1-NEOFORGE

Supplementaries Version

supplementaries-1.21-3.1.0

Moonlight Lib Version

moonlight-1.21-2.18.0

Describe Issue

When launching the game with Supplementaries installed, the game fails to start and says that Supplementaries requires Create 6.0.0. Installing Create does fix the issue, but obviously this isn't meant to be.

Another user on Reddit replicated the issue with only Moonlight Lib and Supplementaries installed, so it is not related to any other mods on the pack.

ok Should be fixed.

Fixed in v3.1.1

REASON:
mods.toml was using the old code from 1.20.1
mandatory = false was removed and added type = "optional" to make the mod Create, an optional mod instead of "required mod"

Thanks for the report. I don't realize my mistake.

TEMP SOLUTION:

TEMP solution is to go inside the JAR using 7zip and go to ~/META-INF/mods.toml

open the file and remove code block for "create". it should be easy for you to find it. then with that, you can launch Minecraft.