What does macOS need?

To understand where these sections come from, you need to understand what macOS is looking for in a disk drive for it to install "properly". macOS put some restrictions on the size and the possibility to even format a partition as HFS+ if some requirements are not fulfilled.
macOS looks for:
  • a GPT formatted disk
  • a EFI partition:
    • FAT32 formatted (not that it matters for it)
    • flagged as EFI System Partition (hex: EF00 in gdisk)
    • is 200MB at least
    • in the same disk where macOS should be installed.
  • 60GB of free space
If any of these are in your target disk, you're good to go, if not, that's the point of this guide.