Best way to run an existing Windows SSD on the M1 chip?

There is no supported version of Windows natively for Apple silicon. There is nothing available for purchase.

Which processor architecture is your "existing Windows SSD" built for? (I'll assume x86-64, but there are other possibilities. Over the years, Windows has been ported to various architectures, including x86-32, x86-64, AArch64, Alpha, Itanium, and some others.)

Because if your existing Windows install is not one built for AArch64, you'll need an emulator. That emulator might be UTM, or maybe some other emulator-capable option. This is processor and system emulation, in addition either to system virtualization, or in addition to something akin to Boot Camp.

Without emulation, you'll need the Windows Insider's version of Windows for AArch64, and some added bits such as Parallels.

Another approach is to host Windows on Azure or such, or on some other computer, and access it remotely.

For what might happen with the future of Windows and licensing and support on Apple silicon, ask Microsoft.

videonoob wrote:

….

The owner of said MacMini M1…

Do you want the owner to have a complex and unsupported solution, and particularly one that you don’t yet understand, and then explain and sustain it for the owner?

….wants to be able to still boot into Windows until he gets accustomed to MacOS Monterey. Given the above items at my disposal, how can I use the M1 architecture to access the Windows OS externally?

Keep the old PC around until y’all are willing to cut it free.

Here's some thinking-out-loud:

Due to the SSD size differences (256GB vs 500GB), the Migration Assistant is out.

Migration Assistant and storage capacities are not relevant here. Unless the storage on the new Mac is under-configured, that is. Then you’re headed for bigger issues.

When emulating Windows virtually on the MacMini M1, would I use Parallels, or UTM?

Emulation and Virtualization are very different. UTM includes both emulation and virtualization support. How well that might work here depends greatly on what was running on the Windows PC, too.

How can I use Parallels to directly access the Windows 10 SSD in an external enclosure?

Go skim the Parallels doc, and skim the UTM doc.

Should I upgrade the PC to Windows 11 first, and then create the virtual machine?

I would suggest keeping the Intel x86-64 system. One supported by Windows.

You might be able to use a KVM switch to switch the keyboard and mouse and the display between systems, to reduce the clutter, pending retirement of the Windows PC here. This’ll take some adapters, as the Mac will be USB-C connectors, and an older Windows PC will usually be using the older USB-A connectors.

You can also set up an SMB Share on Windows, and mount that share from macOS. This to allow common document formats to be accessed and migrated. Or transfer the user files onto an ExFAT or maybe NTFS flash drive, and transfer those manually. This if the Windows migration assistant doesn’t get things going.

I haven't worked on a PC since Windows 98/XP, so any step-by-step guidance is highly appreciated.

Keep the existing Windows PC. Otherwise, you can either gain a whole lot of experience with virtualization and emulation and with whatever wrinkles and bugs and crashes might exist and all this without support, and with Windows, or you can get going with whatever the user wanted to do with macOS.

There re various guides and documenta for folks switching from Windows:

…Mac tips for Windows switchers - Apple Support

TL;DR: I would not suggest adding unsupported systems and emulation to an already complex endeavor.

I'll try again. There is no production version of Windows that will run om a silicon Mac. This includes running Windows in a VM or natively.

In addition, Microsoft does not support installing and running Windows on an external drive.

You can use migration assistant or iCloud or other cloud service to transfer all your data. You could also just manually copy your data to an external drive then connect that drive to your Mac to copy off the data.Transferring data is not an issue. Apps like Microsoft Office will run natively on your Mac. Windows itself will not run on the Mac.

There is no way to run Windows on your M1 Mac.