The IP is 10.91.91.5 and the hostname FQDN is vcsa.vigil.com, and the DNS is a Fortigate Firewall.
This vCenter server was created in VMware Workstation and then pushed to ESXi using vCenter Converter. It was working fine in Workstation but in the ESXi it ran into this issue.
Does it load the page when you try connecting with https://vC-FQDN/ui ?
Do you notice similar issues with other browsers and system? Some times it's a cache issue. Try launching from Google Chrome incognito mode.
I replicated the issue in workstation, this happens when I make Fortigate as my DNS, exactly the same issue. Seems to be a record related issue.
The Launch vCenter page only loads if I go to https://10.91.91.5, it does not load otherwise.
When I load the page via https://vcsa-FDQN/ui I end up with Can't reach this page, server IP address not found, tried both Chromium Edge and Chrome.
Also I did an nslookup from vCenter SSH and the DNS resolution both forward and reverse lookup is resolving fine.
Well...... the SSO part always performs a Redirect to its configured FQDN. If the client cant resolve this FQDN than you cannot log into vCenter. You didn't take notice the redirect within local lan or when start accessing the vCenter by using the FQDN.
If youre outside from your DNS you can edit your local etc/hosts to work around. But dont forget to uncomment the entry when your back in your LAN environment.