This applies to all VMC SDDC's.
vSphere does not support VM Template synchronization. Synchronize the Contents of a Subscribed Library
VMC vCenters can publish entire Content Libraries and sync OVA/OVF files as well as ISO files between the Publisher > Subscriber. This requires the entire Content Library be set for publishing, optionally including authentication.
However, VM Templates (VMTX files) cannot be synced between Publisher > Subscriber.
From Synchronize the Contents of a Subscribed Library:
Export the VM Template in question as an OVF Package, and then publish that OVF package in the Publisher Content Library.