S3 Destinations are not available in Add option of Option Group for SQL BACKUP

I already created an Option Group in RDS and am trying to add Option. But when I try that with the new IAM role, I can't select the S3 bucket from the list. The S3 list is not populating in the drop-down.

The data list (S3 bucket list) from API is coming as I checked with the browser console.

Note: I did the same day before as a test without such an issue and deleted the created IAM role. And I have Admin access to the account.