I’ve been trying unsuccessfully to migrate a Windows 10 Bootcamp installation from my 2019 iMac (iMac19,1) to an external drive (Samsung SSD in an OWC USB-C enclosure).
I can’t find a source for Windows build 1809, so I tried with a fresh install of the latest (1909 I believe). Installation on the iMac went smoothly, but once installed, I couldn’t get Sysprep to complete successfully. The log gives errors about preinstalled apps/services like xboxonesmartglass not being installed for all users. (paraphrasing)
I used Winclone to migrate this installation (without Sysprep) to the external SSD. Holding Option while booting shows me the external drive as “EFI”. Selecting it takes me to the Windows logo, but then I get either “Your PC ran into a problem and has to restart” or a blank blue screen. I can’t seem to access Safe Mode by holding shift.
I did precisely the same thing about a month ago, offloading my BootCamp from my macBook to a Samsung SSD. I wish I could remember the specific details, but I did have more than a bit of trouble. From memory, I used sysprep in Win10, which pretty much eliminated all of the parameters in Win10. At least 2 or 3 times, I went to the winClone log to discover a problem that I was able to correct. Finally, I did get it to complete under WinClone. Once the WinClone image was complete, I restored it to a exFat partition on my Samsung SSD, while leaving the 2d exFat partition untouched. The 2d partition allows me to transfer files from macOS to Win10. Winclone reformatted the 1st exFat partition under NTFS and loaded the image. It works nicely now with my macBook. It loads like any BootCamp partition. It even works without any modification with my partner’s iMac ‒ no need for extra drivers. Convinces me that Win10 works better with Mac machines than with any other - go figger!
I did have trouble with sysprep. I had to search the Web a bit to find answers. Once it completed OK, I did WinClone and had some issues. These were noted in the WinClone log and I was able to resolve them.