The Migrate Real-Time screen allows selecting multiple objects, but there is a character limit on the field.
If the combined selected object names exceed the limit, the system will show a warning.
Admins should select only the required objects to stay within the field limit and avoid errors. Here, the recommended object selection is 10.
PS: View Drag, Drop & Upload Files to Amazon S3, a Salesforce AppExchange app for moving files from Salesforce to Amazon S3: https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3000000B5ZPqEAN