So the problem we were facing as we were using manual made config like these:

import Amplify from 'aws-amplify';
Amplify.configure(
    Auth: {
        identityPoolId: 'XX-XXXX-X:XXXXXXXX-XXXX-1234-abcd-1234567890ab', //REQUIRED - Amazon Cognito Identity Pool ID
        region: 'XX-XXXX-X', // REQUIRED - Amazon Cognito Region
        userPoolId: 'XX-XXXX-X_abcd1234', //OPTIONAL - Amazon Cognito User Pool ID
        userPoolWebClientId: 'XX-XXXX-X_abcd1234', //OPTIONAL - Amazon Cognito Web Client ID
    },
    Storage: {
        bucket: '', //REQUIRED -  Amazon S3 bucket
        region: 'XX-XXXX-X', //OPTIONAL -  Amazon service region
    }
);

these was working fine in the older version but in aws-amplify^4.3.18 this was breaking. here you can see they say only identityPoolId and region is required but in new version userPoolId and userPoolWebClientId is required to stop the Error