I run ESXi 6.7 in my Lab and tried to install an ubuntu vm into it.
... snip ...
==> utest: Retrieving ISO
==> utest: Configuring output and export directories...
==> utest: Creating floppy disk...
utest: Copying files flatly from floppy_files
utest: Copying file: /tmp/packer/1611091651/preseed.cfg
utest: Done copying files from floppy_files
utest: Collecting paths from floppy_dirs
utest: Resulting paths from floppy_dirs : []
utest: Done copying paths from floppy_dirs
==> utest: Uploading Floppy to remote machine...
utest: packer554707513 1.41 MiB / 1.41 MiB [=========================================================================================================================================] 100.00% 0s
==> utest: Remote cache was verified skipping remote upload...
==> utest: Creating required virtual machine disks
==> utest: Building and writing VMX file
==> utest: Registering remote VM...
==> utest: Starting virtual machine...
==> utest: Connecting to VNC...
==> utest: Error handshaking with VNC: no suitable auth schemes found. server supported: []byte{0x1}
==> utest: Waiting 3.268086874s to give VMware time to clean up...
==> utest: Stopping virtual machine...
==> utest: Destroying virtual machine...
Build 'utest' errored after 20 seconds 189 milliseconds: Error handshaking with VNC: no suitable auth schemes found. server supported: []byte{0x1}
...snip...
There is no VNC on ESXi 6.7. Does some else faced same issues?