Apache mod_proxy RewriteRule to AWS S3 object yields 403 Forbidden

Question

I'm looking for an answer on how to rewrite an AWS S3 URL on my website, using Apache mod_proxy.

Here's the rule I'm using in my .htaccess file on my website :

<IfModule mod_proxy.c>
RewriteEngine On
RewriteRule ^img_test/([a-z-]+)-([0-9]+)\.png$ https://[MY-BUCKET].s3.eu-west-3.amazonaws.com/[MY-BUCKET-SUBFOLDER]/img/c/$2.png [P]
</IfModule>

On my AWS S3 Bucket, I''ve set all "Block public access" settings to Off, and implemented the following bucket policy :

{
    "Version": "2012-10-17",
    "Id": "S3_Policy",
    "Statement": [
        {
            "Sid": "PublicReadGetObject",
            "Effect": "Allow",
            "Principal": "*",
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::[MY-BUCKET]/*"
        }
    ]
}

As well as the following CORS rule :

    {
        "AllowedHeaders": [
            "*"
        ],
        "AllowedMethods": [
            "GET",
            "PUT",
            "POST",
            "DELETE"
        ],
        "AllowedOrigins": [
            "https://www.my-website.com"
        ],
        "ExposeHeaders": []
    }
]

However, when I call the following URL : https://www.my-website.com/img_test/test-5.png, I'm getting a 403 Forbidden error, instead of getting the contents of the file located on my AWS S3 bucket.

If I use the same .htaccess rule, but without the [P] flag, the URL redirects to https://[MY-BUCKET].s3.eu-west-3.amazonaws.com/[MY-BUCKET-SUBFOLDER]/img/c/5.png.

I suspect there might be something more to configure on my AWS S3 bucket, but I'm at a loss to figure out exactly what.