Using Partitioned External Harddrive with Bootcamp
If you installed the Windows Support Software, then Windows should be able to recognize Mac OS Extended (Journaled) formatted volumes. AFAIK, Windows can not recognize APFS volumes without third party software. If an external HDD contains a ExFAT formatted partition, then any version of Windows running on a Mac can access the volume. Although, older versions of Windows may need a to have an update installed. Here, I assume the external HDD is using a Master Boot Record (MBR) partition table or GUID Partition Table (GPT).

Note: There are newer Macs running Windows that can access APFS containers for the purpose of selecting the system to use to start up your computer.