I'll thank you now for your efforts to help the community. I've read through this thread and applied all the things...

"Adding Trusted Target failed - Certificate Status check failed: Failed to resolve target name"

That is the error I got after the appliance install, and thats what I still get after adding Domains=sub.domain.local

I note for the newbies that the domain value needs to be the domain of the vcenter server.

After editing the file I restarted :

systemd-networkd

systemd-resolved

vmware-shd

Still no joy.

Fixed IT!!! -

I change the DNS IP addresses in that file to be the same as those used by vcenter server. restarted the 3 services above and Bob's my uncle.