Partial solution

As I've alredy try using Minio (S3) disk with a domain name, and a valid Cloudflared SSL certificate (like https://minio.mydomain.com/bucket-name/...), I've get constantly error message for JUST retriving files and NOT for uploading files.

So I've decide to use OpenSSL certificates, and added to MinIO to serve as HTTPS with a local IP address (https://192.168..:9000) instead of the domain (which for sure will make a security gap if the app is served in a reverse proxy like Cloudflared Tunnel), but will work for now.

Resume

// config/filesystems.php
'custom-minio-s3-disk' => [
  # Configurations added
  'ssl.certificate_verification' => false, # Needed to skip console connection refuse
  'http' = [ 'verify' => false ],
]

// .env
CUSTOM_KEY=...
CUSTOM_SECRET_KEY=...
CUSTOM_BUCKET=bucket-name
CUSTOM_ENDPOINT=https://192.168..:9000 # Using HTTPS with a OpenSSL Certificate

I guess there's some good reason for this error to happen.