You are correct, vCenter on Windows has been deprecated on vSphere 7. You can still perform the upgrade but in your case will be a migrate. Migrate means that your vCenter will move to version 7 and a new appliance will be deployed.
No worries about the new appliance being created as IP Details, FQDN, and Configurations and all will be retained there so there is no extra work. Refer to the following section for all the details: https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vcenter.upgrade.doc/GUID-9A117817-B78D-4BBE...
If you have some doubts feel free to ask me 
