In a simplistic high-level view: DB backups are taken in two distinct ways: logical backups or physical backups. Logical backups work by reading the data from database, they are slower and might cause some locks on some tables and/or rows while taking backups so they might not be suitable and good for system performance in some cases.
Physical backups are faster and impose minimal impact on system but requires physical access to database subsystems (OS, Disks, Volumes).
RDS as a managed service does not allow access to hardware or operating system thus customers can not use physical backup tools. These kind of backups are provided within the service itself (as snapshot based backups in RDS).
Logical backups are easier and flexible because they only need access to database. If you can read, you can do a logical backup. The simplest example is using mysqldump and variants to take logical backups of MySQL/Aurora RDS.
Long story short customers are limited in physical backups solutions but more flexible in logical tools. If this requirement is about MSSQL-RDS, yes customer can use this feature to import/export .bak files to backup individual databases in MSSQL.
For an MSSQL customer the link that you shared may help.
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