How to create Mysql rds instance from a encrypted snapshot stored in s3 bucket.

Its not possible to restore the RDS export in S3. The export isnt designed to be able to restore back to an RDS instance once you have exported to S3.

When you export a DB snapshot, Amazon RDS extracts data from the snapshot and stores it in an Amazon S3 bucket. The data is stored in an Apache Parquet format that is compressed and consistent.

You can export all types of DB snapshots—including manual snapshots, automated system snapshots, and snapshots created by the AWS Backup service. By default, all data in the snapshot is exported. However, you can choose to export specific sets of databases, schemas, or tables.

After the data is exported, you can analyze the exported data directly through tools like Amazon Athena or Amazon Redshift Spectrum.

https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_ExportSnapshot.html