Firstly go through steps: Install Windows 10 to External Drive on Macbook The following steps will allow you to have one or more macOS installation in a single APFS volume on the external drive. Install macOS Boot into Windows and resize Windows partition to make space for macOS installations. Create new partition in Windows for macOS installations. Boot into macOS and open Disk Utility. Format newly created partition to APFS. Download macOS installation from the macOS App Store....
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Install Windows 10 to External Drive on Macbook
Having an installation of Windows availiable is often really useful! However, I don’t quite have enough space to dedicate an internal partition on my 2018 MacBook Pro. Instead, I wished to install Windows to an external drive to give me the benefits of having a Windows install without losing storage space for my primary macOS installation. Disable Secure Boot and Enable Boot to External Drives Steps widely documented. Create Windows 10 Installation USB Using a Windows machine create a Windows 10 installation USB using the Windows 10 installation media creation tool...