Yes, that's the web based HTML5 client.
If you've vCenter i recommend to connect to vCenter for managing your hosts.
https://vcenter_server_ip_address_or_fqdn/vsphere-client.
You need to use the vSphere webclient or the HTML 5 client.
vSphere 6.5 and later, the C# client will not be available.
Yes, that's the web based HTML5 client.
If you've vCenter i recommend to connect to vCenter for managing your hosts.
https://vcenter_server_ip_address_or_fqdn/vsphere-client.
Since version 6.0 you can use an old thick C# client to connect to your ESXi hosts.
Just use IP address to access HTML management interface of the ESXi host. The same applies to vCenter (again, use IP address or FQDN of the system to access HTML interface).
Starting with vSphere 6.5 and later the C# client will not be available anymore.
You can read more here VMware Knowledge Base
RickVerstegen is correct, ESXi 6.7 does not support old thick client. Start using webclient from now. Just enter your host's IP/Name or vcenter's IP/Name into your browser and begin. Thanks