On my Early 2015 MacBook Pro (Monterey) I successfully created bootable Windows 10 on a partition on an external SSD using the method given in Answer 1 here:
I can boot into Windows 10 from this external SSD on my MacBook Pro (Monterey, latest) and a 2017 iMac (Ventura, latest) and all works fine (Windows adjusts to the new hardware).
However, on my 2018 Mac mini, Windows will not boot from this SSD. The Windows logo displays, an "attempting repair" message then displays, but then the display goes black, the Mac mini stays on, but nothing happens.
Interestingly, using the 2018 Mac mini, and using the same method, I successfully created bootable Windows 10 on an old HDD. It works OK, but is of course painfully slow.
So, on my Mac mini, I then tried installing Windows 10 on a new Samsung T7 SSD using the exact same method. However, the installation process fails to start. I see the Windows logo, which shows for about 90s, then nothing.
I subsequently tried another method using VirtualBox, but again, the the installation process fails to start. On booting to complete installation, the Windows logo shows for about 90s, then the display goes black and nothing happens, but the Mac mini stays on.
I have tried setting the Mac mini's Secure Boot to "no security" but it makes no difference. And "allow booting from external or removable media" is ON.
The Mac mini runs Windows 10 perfectly from Bootcamp on its internal SSD, but I wanted to run Windows from an external SSD as I'm running out of storage.
I tried another method using Rufus but again the Mac mini would not boot the installation, while the iMac did.
I cannot understand why the above method works on an old 2.5" HDD (in an Orico enclosure) but not a SSD, or why the mini cannot boot into Windows while my other Macs can.
I'm guessing it has something to do with the T2 chip?