Welcome. First thing's first, you keep saying "ESX" but it's not ESX. It's ESXi. They were two very different hypervisors. One letter difference but big differences.
Second, if you can't ping the ESXi IP address from the client computer where you're attempting to access it via a web browser, you have network connectivity issues. You are not required to manually adjust any firewall rules on ESXi after installation to access the embedded host client at https://FQDN/ui. And SSH has nothing to do with this form of access as they are two separate protocols.
Thanks! You were right. The problem was caused by the wrong GW address