Bug description and reproduction steps

Tested with https://modrinth.com/mod/useful-backpacks/version/3.0.1.126

You're also using the old fabric ID in your fabric.mod.json. It should be replaced with fabric-api.

https://github.com/MC-U-Team/Useful-Backpacks/blob/1.21.1/fabric/src/main/resources/fabric.mod.json#L32

Log files and Screenshots

n/a

Used minecraft version

1.21.x

Used forge or fabric version

Fabric Loader 0.16.10

Used mod version

3.0.1.126

Fixed in this version: 3.0.1.127