HTTP/2 requests to Spring Boot on ECS behind AWS NLB fail with PROTOCOL_ERROR (HTTP/1.1 works fine)

After upgrading our application to Spring Boot 4.1.0, requests started failing once the service was running behind an AWS Network Load Balancer (NLB) configured with a TLS listener. The same build worked before the upgrade. Our setup terminates (offloads) TLS at the NLB via a TLS listener, and the connection from the NLB to the target group is plain, non-TLS.