Restore only one database in an AWS RDS Sql Server instance
When you restore from an RDS snapshot, you will create a new RDS instance. You do not restore "into" an existing RDS instance.
So you would restore the full RDS instance and use it to:
- replace the "old" instance (all databases), or
- pull the single database you want from the restored RDS instance and copy it's data to the original RDS instance.
If you are that concerned about individual databases, then you could keep the individual databases on their own RDS instances.
I believe it is now possible to restore an individual database to the same instance. The process is described here https://www.sqlshack.com/recover-data-in-aws-rds-sql-server/. Automated backups use storage volume snapshots, so I don't think it would work in that scenario.