Here a the files and guides I used for the installation of OS X Mojave on HP EliteDesk 800 G3 Mini

Product Name : HP EliteDesk 800 G3 Mini 65W / HP EliteDesk 800 G3 Desktop Mini 65 W

Product N° 1ND88ET#ABF

• CPU : Intel Core i5-6500 3.2 GHz
• GPU : Intel HD Graphics 530 (Dual Display Port, HDMI)
• Memory : 2 Slots DDR4-2133
• Storage : PCIe NVMe 256 GB, PCI-E Gen3 x 4, Turbo Drive G2 Toshiba KXG50ZNV256G
• Ethernet : Intel I219LM Gigabit Network Connection LOM
• Wireless LAN : Intel 7265 802.11ac 2x2 Wi-Fi with Bluetooth M.2 Combo Card
• Audio : Conexant CX20632 (Internal Speaker, 2 audio out front ports)

Wireless LAN : Replaced Intel M.2 Combo Card with M.2 Combo Card for Lenovo Y50-70 with Broadcom Chipset BCM94352Z NGFF 802.11ac Wifi + Bluetooth 

• Conexant CX20632 requires VoodooHDA.kext which is incompatible with HDMI Audio. If you wish to use HDMI Audio output replace VoodooHDA.kext with AppleALC.kext and inject audio channel 11.
• Skylake Sleep issue cause reboot on wake. Disable sleep in Engergy Settings.

This guide isn't a Vanilla install guide since I couldn't get the BCM94352Z to work with kexts installed on the EFI partition For a Vanilla install, simply skip the Wireless LAN part and use a Wifi-Bluetooth USB Key instead

• Disable Fast Boot
• Enable USB boot
• UEFI Boot order, make sure your USB device is first to boot
• Secure Boot : Legacy Support Enable and Secure Boot Disable
• Disable : Virtualization Technology for Directed I/O (VTd)
• Enable : M.2 SSD (if you use a NVMe SSD)
• Uncheck M.2 WLAN/BT (if you don't have a compatible M.2 Combo Card)
• Disable Wake on lan
• Set Video Memory to 64 MB

Create an USB Key with Mojave manually or using a software like Diskmaker

I used Clover V2.4 Release 4798

Customize installation

NOTE : These are the settings are for motherboards doesn't support UEFI.

• Uncheck Clover for UEFI booting only
• Uncheck Install Clover in the ESP
• Boot Sectors :
  • Check Install boot0af in MBR
• Clover for BIOS (legacy) booting
  • Clover EFI 64-bits SATA
• Uncheck Bios Drivers, 64 bits
• Uncheck FileVault 2 Bios Drivers, 64 bit
• UEFI Drivers check :
  • DataHubDxe-64
  • FSInject-64
  • SMCHelper-64
  • VBoxHfs-64
  • ApfsDriverLoader-64
  • EmuVariableUefi-64
  • NvmExpressDxe-64 (if you have a nvme SSD)
  • OsxAptioFix3Drv-64
  • OsxFatBinaryDrv-64
• FileVault 2 UEFI Drivers check :
  • AppleImageCodec-64
  • AppleKeyAggregator-64
  • AppleKeyFeeder-64
  • FirmwareVolume-64

Download Clover Configurator and copy it on the installation key.

Boot on USB and install Mojave. I chose to format the disk in APFS.

During the installation the system will reboot a couple of times. When the system reboot on the clover screen make sure you Inject Intel GFX and set Input FakeID : 0x19120000.

If you don't want to enter these settings on clover boot screen you can edit the config.plist from your installation key and set them.

Copy Clover Configurator and use it to mount the EFI Partition of your system.

You can mount manually your EFI Partition. On a terminal window Identify the EFI partition on your disk with the command

• diskutil list Create a mount point
• mkdir /Volumes/efi Mount partition
• sudo mount -t msdos /dev/disk0s1 /Volumes/efi

Copy the EFI folder on your Installation key on the EFI of your Add the following kext in /EFI/kexts/Other

• Lilu.kext (https://github.com/acidanthera/Lilu)
• VoodooHDA.kext (https://sourceforge.net/projects/voodoohda/)
• IntelMausiEthernet.kext (https://bitbucket.org/RehabMan/os-x-intel-network/downloads/)
• WhateverGreen.kext (https://github.com/acidanthera/WhateverGreen)
• FakeSMC.kext (https://github.com/RehabMan/OS-X-FakeSMC-kozlek)
• USBInjectAll.kext (https://github.com/RehabMan/OS-X-USB-Inject-All)

Use the following guide to generate a patched ssdt for CPU Power Management

https://www.tonymacx86.com/threads/quick-guide-to-generate-a-ssdt-for-cpu-power-management.177456/

Use the following guide to generate a patched ssdt for injecting USB Port

https://www.tonymacx86.com/threads/guide-creating-a-custom-ssdt-for-usbinjectall-kext.211311/

If you have a compatible M.2 Combo Card use the following guide

https://www.tonymacx86.com/threads/broadcom-wifi-bluetooth-guide.242423/

ACPI Section

Add the following DSDT Patches

• Rename HDAS to HDEF

  • Find : 48444153
  • Replace with : 48444546

• Change SAT0 to SATA

  • Find : 53415430
  • Replace with : 53415441

Check :

• FixAirport
• FixHDA
• PluginType

SortedOrder

• ssdt.aml (patched ssdt for CPU generated)
• ssdt-UIAC.aml (patched ssdt for USB Injection generated)

Boot Section

Check :

• dart=0
• -disablegfxfirmware
• NeverHibernate
• HibernationFixup

Boot argument : -lilubetaall

If you have a compatible M.2 Combo Card use this boot argument (Replace FR by your country code)

-lilubetaall brcmfx-country=FR

Graphics Section

• Inject Intel
• ig-platform-id : 0x193B0005

Kernel and Kexts patches Kexts to patches

Name : AppleAHCIPort Find : 45787465 726E616C Replace with : 496E7465 726E616C

Name : com.apple.driver.AirPort.Brcm4360 Find : 81F952AA 00007529 Replace with : 81F952AA 00006690

SMBIOS use iMac17,1 (Late 2015)

If you use the attached config.plist generate a new Serial Number and a new SmUUID

** UPDATE - Catalina *** New EFI folder for Catalina Installation. I switched my old Elitedesk Intel Core i5-6500 for a i5-7500T but this EFI should also work for i5 6500 models.