Client IP preservation is only supported when NLB and targets are in the same VPC, not for targets in peered VPC or on-premises.
There is no DSR as you correctly mentioned, the AWS SDN handles the connection in such a way that the Client IP is preserved and traffic is still (symmetrically) routed via NLB.
"When client IP preservation is enabled, targets must be in the same VPC as the Network Load Balancer, and traffic must flow directly from the Network Load Balancer to the target."
Cannot select a target group with alb target type when creating an application load balancerAccepted Answerasked 3 months ago
Restricting incoming NLB traffic to internal IP addressesAccepted Answerasked 2 years ago
AWS NLB security groupasked 9 months ago
NLB TARGET IP OVER PEERED VPC CONNECTIONAccepted Answerasked 3 months ago
NLB IP preservation over peering target groupasked 2 months ago
Why can an instance in a target group not reach itself via NLB?Accepted Answerasked 2 years ago
How does it work differently per target group?Accepted Answerasked 4 years ago
Handling of target IP addresses in rule for outbound endpointasked 3 years ago
Proxy Protocol V2 with Disabling client IP preservation in NLB Target groupsasked 11 days ago
Client IP Preservation for Network Load Balancer endpoints for Global Acceleratorasked 8 months ago