The OBTU Server is currently unable to synchronize with the SDDC Manager specifically during patch operations. Normal synchronization activities appear unaffected; however, when initiating or executing patch workflows, the server fails to establish or maintain the required sync state with the SDDC Manager.
VMware Cloud Foundation 5.1
SDDC Manager 5.1 doesn't have support for the async patching using GUI.
Async Patch tool should be used as per the article here: Apply an Async Patch to VMware Cloud Foundation in Offline Mode to download and enable patches in SDDC manager.
Async patch tool does not support offline depot.