Condition There is a MacBook Pro Early 2015 without an internal drive. It is required to organize macOS and Windows 10 on it in the dual-boot version from one external drive.
Relevance . The internal storage of modern MacBooks is represented by the PCI-E SSD in the proprietary Apple form factor. Non-original 128–256 GB can be purchased at a price in the range of 5–10 thousand rubles. [ 1 , 2 ]. On the other hand, if there is a sufficiently fast external drive (or low demands on its speed), you can boot from it.
Obstacles . Makos cannot be delivered without (a) an additional drive for the installer and (b) a second poppy to write this installer to this additional drive (plus the file with the installer itself) —the instruction from Apple .
Mac OS 10.13 High Sierra refused to be installed on an external drive. On the other hand, 10.10 Yosemite and older will not stand on modern poppies.
When makos is installed, the standard way to install Windows from under it is Boot Camp. However, it does not allow installation on an external drive. It would be possible to write the Windows installer to an additional drive (using standard macos tools, using UNetbootin, Rufus, or other means), but it also will not allow installation on an external drive.
The decision . (a) Instead of the bootcamp, we manually prepare a suitable partition on the drive [ 3 , 4 ], then (b) instead of the Windows installer, use the WAIK tool to upload the loader and installation files [ 5 ] to the drive; (c) we reinstall Windows by booting through the clamped Option into the EFI Boot; (d) install the driver package from the WindowsSupport directory (which we get by rebooting into MacOS, opening the bootcamp and finding it in the menu “Download the latest Windows support software from Apple”). Tested - works.
If you need more detailed instructions, write in the comments.