I've been looking into this a bit and it seems that currently the Amplify v2 does not support this.

Eg. the only bundling config I could find when you use defineFunction is minify (see https://github.com/aws-amplify/amplify-backend/blob/main/packages/backend-function/src/factory.ts#L235-L242)

On the other hand it seems that the source maps are turned on by default https://github.com/aws-amplify/amplify-backend/blob/main/packages/backend-function/src/factory.ts#L491

Do you use latest version of Amplify?