Once Windows Deployment Services is installed and running, locate the folder where WDS is installed. My install is in D:\RemoteInstall.

1. Rename pxeboot.n12 in D:\RemoteInstall\Boot\x64 to pxeboot.0.
2. Rename abortpxe.com in D:\RemoteInstall\Boot\x86 to abortpxe.0.
3. Download syslinux. I used version 5.04. Your mileage may vary with other versions.
4. From the syslinux archive, extract core\pxelinux.0, com32\menu\vesamenu.c32, com32\modules\chain.c32, memdisk\memdisk to D:\RemoteInstall\Boot\x86 and D:\RemoteInstall\Boot\x64.
5. Rename pxelinux.0 to pxelinux.com in both directories.
6. Create the following directories:
   • D:\RemoteInstall\Boot\x64\Linux
   • D:\RemoteInstall\Boot\x64\pxelinux.cfg (this is a directory, not a file)
   • D:\RemoteInstall\Boot\x64\Linux
   • D:\RemoteInstall\Boot\x64\pxelinux.cfg (this is a directory as well)
7. Open a command prompt with Administrator permissions and issue the following commands:

   wdsutil /set-server /bootprogram:boot\x86\pxelinux.com /architecture:x86
   wdsutil /set-server /bootprogram:boot\x64\pxelinux.com /architecture:x64
   wdsutil /set-server /N12bootprogram:boot\x86\pxelinux.com /architecture:x86
   wdsutil /set-server /N12bootprogram:boot\x64\pxelinux.com /architecture:x64
   

   
   

8. Create a two files called default and graphics.conf in D:\RemoteInstall\Boot\x64\pxelinux.cfg and D:\RemoteInstall\Boot\x86\pxelinux.cfg
9. Edit default and add the following text for the default menus:

   DEFAULT      vesamenu.c32
   PROMPT       0
   
   MENU TITLE PXE Boot Menu
   MENU INCLUDE pxelinux.cfg/graphics.conf
   MENU AUTOBOOT Starting Local System in 8 seconds
   
   # Option 1 - Exit PXE Linux & boot normally
   LABEL bootlocal
         menu label ^Boot Normally
         menu default
         localboot 0
         timeout 80
         TOTALTIMEOUT 9000
   # Option 2 - Run WDS
   LABEL wds
   	 MENU LABEL ^Windows Deployment Services
   	 KERNEL pxeboot.0
   # Option 3 - Exit PXE Linux
   LABEL Abort
   	MENU LABEL E^xit
   	KERNEL abortpxe.0
   

10. Edit graphics.conf and add the following text for the default menus:

    MENU MARGIN 10
    MENU ROWS 16
    MENU TABMSGROW 21
    MENU TIMEOUTROW 26
    MENU COLOR BORDER 30;44		#00000000 #00000000 none
    MENU COLOR SCROLLBAR 30;44		#00000000 #00000000 none
    MENU COLOR TITLE 0 		#00269B #00000000 none
    MENU COLOR SEL   30;47		#40000000 #20ffffff
    MENU BACKGROUND background.jpg
    NOESCAPE 0
    ALLOWOPTIONS 0
    

11. Place your ISOs or image files in D:\RemoteInstall\Boot\x64 or D:\RemoteInstall\Boot\x86.
12. Edit D:\RemoteInstall\Boot\x64\default or D:\RemoteInstall\Boot\x86 (depending on the architecture of your OS install) and add the following example text:

    LABEL LABELNAME
    MENU LABEL LABELNAME
    Kernel memdisk
    append iso raw initrd=FILENAME.iso
    

    Your filename is the name of your ISO file.

Many distros will have their own way of getting this to boot correctly. For example, while Debian provides a relatively easy path to add a network install, with Ubuntu 20.04, Canonical has taken steps to push people to alternative ways to easily do a traditional network install. Much Googling is to be had. See PXE config examples.