CORS Request to S3 Accepted for File Display but Not for Load by Javascript Library

I'm developing a small javascript browser script that retrieves files from S3.

I can display the images in an tag without any issue after requesting a SignedUrl to S3. To do so I updated the CORS policy on S3:

[
    {
        "AllowedHeaders": [
            "*"
        ],
        "AllowedMethods": [
            "GET",
            "HEAD",
            "PUT",
            "POST",
            "DELETE"
        ],
        "AllowedOrigins": [
            "*"
        ],
        "ExposeHeaders": []
    }
]

However when I want to use the same URL to extract the EXIF data (using ExifReader), I get an error message about CORS policy:

Access to fetch at '*SIGNEDURL*' from origin 'null' has been blocked
by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. 
If an opaque response serves your needs, set the request's mode to
'no-cors' to fetch the resource with CORS disabled.

I don't understand the difference in the behaviour of both. Can someone help?

Thank you

from CORS Request to S3 Accepted for File Display but Not for Load by Javascript Library