IMHO Windows 10 can only boot from the first partition of your HD drive.I've spent a lot of time trying to figure out how to clone Win10Pro from the spinning drive of my early-2009 24" iMac onto an external SSD-drive without the convenience of CCC, TDM, FireWire etc. ...
No success with PartitionWizard9, since the bootable CD-version of PartitionWizard wouldn't want to boot at all and a PartitionWizard installation located on the spinning drive got stuck at "grub" in the process of rebooting ...
You will need a To-Go installation to run from an external drive.
Another solution is to clone to a Thunderbolt drive. That TB drive is recognized as Disk 0, even before the internal none.
Windows 11 has not that limitation.