Is it possible to create Aurora Replicas on the cross-region replica cluster?

Yes, you can create Aurora Replicas within a cross-region replica cluster in Amazon Aurora Global Database.

What is Amazon Aurora Global Database? How do you create an Amazon Aurora Global Database?

Amazon Aurora Global Database is an extension of Amazon Aurora that lets you create a single Aurora database spanning multiple AWS regions, low-latency global reads (by placing readers closer to users),fast cross-region disaster recovery (in case the primary Region fails).

Does Amazon Aurora encrypt your data in transit and at rest?

Encryption at rest:
Aurora uses AWS Key Management Service (KMS) to encrypt your data stored on disk, including automated backups, snapshots, and replicas. You can enable encryption when you create the Aurora cluster.
Encryption in transit:
Aurora uses Transport Layer Security (TLS) to secure data in transit between the client application and the Aurora database instance. You can require your client connections to use SSL/TLS to ensure data is encrypted while moving over the network.

Does enabling PITR impact the performance or availability of a DynamoDB table?

No, PITR can back up tables with hundreds of terabytes of data with no impact on the performance or availability of the DynamoDB table data.

How long can DynamoDB keep backup data using PITR?

Maximum Thirty Five Days.