To create an UEFI-bootable USB installer for ESXi 6.5 (or newer) on a Mac, follow the steps below.

First, you'll need an USB flash drive. Any recent drive will be large enough (you'll need at least 512MB). Also, download the latest ESXi installer ISO from My VMWare. You probably need a My VMWare account.

With the prereqs in place:

1. Insert the USB flash drive in the Mac and start up Disk Utility.
2. Erase the USB flash drive and choose to format it:
   • Partition map = MBR
   • Filesystem = FAT32
   Give it a descriptive name of your choosing.
3. After erasing the drive, we still have to mark the one partition on it as "active". Disk Utility does not support this and needs to be done using Terminal:
   1. List all volumes mounted. We need this to figure out the identifier for the USB drive:

      diskutil list

      The identifier will be something like "/dev/disk2s1"
   2. Next, unmount the USB drive (note: this is not the same as eject!):

      diskutil unmount /dev/diskXsY

      Again, don't forget to replace X and Y with the proper numbers, obtained from the first command.
   3. Start up the command-line partioner fdisk in interactive mode (you'll need administrative privileges for this):

      sudo fdisk -e /dev/diskX

   4. At the prompt, type this in order:
      1. Flag the first partition on the volume as active and bootable:

         fdisk: 1> f 1

      2. Write the changes:

         fdisk: 1> write

      3. Exit fdisk:

         fdisk: 1> quit

   5. Remount the USB drive again.
4. Mount the ESXi installer ISO (double-click it).
5. Copy the entire contents of the ISO in the root of the USB drive.
6. On the USB drive, rename the file ISOLINUX.CFG to SYSLINUX.CFG.
7. Open the file SYSLINUX.CFG using a text editor (TextEdit). Do not use Word as it will mess up the contents.
8. In the file, look for the line starting with APPEND -c boot.cfg and append -p 1 on it, so it reads:

   APPEND -c boot.cfg -p 1

9. Save and close the file. Unmount the ISO and USB drive. It is now ready to be used in an UEFI-enabled computer or server.