No, that is a bad idea, if you upload a text file as an attachment, it’s an upload as well, it will cause confusion. And text in a post is stored into the database. So I’m sticking to the term uploads.
If your uploads are on S3, they are not included in backups. In that case the backups only contain a copy of the database. It does not matter whether your backups are local or on S3.
If your uploads are not on S3, they are included in the backups. In that case the backups contain a copy of the database, and a copy of the uploads. It does not matter whether your backups are local or on S3.
If you are storing something on S3, be it uploads or backups of the database, they will not get lost if your DO droplet gets hacked or damaged. So I don’t see your point.
Since your posts are about backups and not about file and image uploads, I’m moving these to another topic.