cat /etc/hosts file shows same FQDNs for the platform nodes as per above which is platform1, platform 2 and platform3This is not a product issue.
FQDNs are not required for the VCF Operations for Network deployment, but you should configure DNS records for IP addresses consumed by Platform and Collector VMs on their respective DNS Servers.
Refer to documentation for VMware Cloud Foundation 9.0 for Deploying VCF Operations for Networks.