Best approach for: Dual boot Mac OS and Win 10 And shared files volume
Steps to do a clean install of macOS and Windows

To do a clean install of the current versions of macOS and Windows, preform the following steps.


Boot to a macOS installation media. For example, this could be a Mojave recover volume, internet recovery or a installation flash drive.
Use the Disk Utility to erase the drive and create a single APFS volume.
Install Mojave to this volume.
Use the Boot Camp Assistant to install Windows 10. Include space for the MS-DOS (FAT) or ExFAT volume to be shared.


Steps to create a shared volume


  This is to be done after installing macOS and Windows.


To create a MS-DOS (FAT) or ExFAT volume to be shared, preform the following steps.


Under Windows 10, open Disk Management. Highlight the BOOTCAMP volume and select Shrink Volume…, as shown below.


Select the desired size, as shown below. Next, select the Shrink button,


Highlight the unallocated space and select New Simple Volume…, as shown below.


When the image shown below appears, select the Next button.


When a image similar to the image shown below appears, select the Next button.


In desired select a different drive letter, then select the Next button.


Select FAT32 and enter a volume label, as shown below. When finished select the Next button.


When a image similar to the image shown below appears, select the Finish button.


The result is shown below.


If you wanted ExFAT format, then restart back to macOS. Use the Disk Utility to erase the volume. Enter a name and ExFAT format, as shown below. When finished, select the Erase button.




Note about the Golden Rule

There is a Golden Rule which can be loosely stated as:


  Never change the partitioning on a Mac from Windows.


In this case, the Golden Rule does not apply for the following reasons.


There no Mac OS Extended volumes on the drive. 
Windows is installed to UEFI boot.