The problem is the usb. If you want to run windows from a removable drive you need a special installation, called "Windows To Go".

You can install it with rufus: https://www.digitalcitizen.life/install-windows-to-go/

Fun fact: Windows will overwrite GRUB if you install Windows after Linux or otherwise perform an action that allows it to mess with the boot loader.

Windows on an external drive isn't officially supported if I remember right. Your screenshot seems to support that.

Honestly, I'd be leery of installing an OS on an external drive as they tend not to age well with heavy use.

Are you trying to necro a laptop with a dead drive? If so, depending on the model, it might just be worth replacing the internal drive so then you can go ahead with your dual boot plan.

Also, quick tip, install windows, then disable fast startup in windows, then disable safeboot in your bios. Otherwise, when it comes time to install mint, you might hit issues with windows saying "NO, MY DRIVE".

If you install mint and get no grub screen, just boot mint with your live usb and look up repairing grub - should be nice and easy.

Afaik most guides suggest setting up linux after windows because of some bootloader stuff. So if you already have linux installed I would suggest setting up a virtual machine if you don't need running windows on raw hardware.

Microsoft is being a dick. Booting from an external USB-attached SSD works fine once you work around the installer limitations.

When I did this I ended up basically partitioning the disk manually with diskpart and installing Windows manually using the command prompt. I used this blog post to guide me:

https://web.archive.org/web/20230810073949/https://decryptingtechnology.blogspot.com/2015/09/install-windows-10-on-usb-external-hard.html#!https://web.archive.org/web/20231204195111/https://decryptingtechnology.blogspot.com/2015/09/install-windows-10-on-usb-external-hard.html

But I remember I had some issue that made me start over.... what the heck was it. Something like the modern Windows 10 image being larger than what the author had encountered. Ah - I think the issue was the WIM file was over 4GB and wouldn't fit on the authors 4096 MB "Recovery Image" partition. So make that one larger (check the iso for the wim file's size) if you plan to create a recovery partition.

Another bookmark I made at the time was this, I think it was mainly for the command listing the SKUs supported by the WIM file, but no guarantees, it's been a while: https://gist.github.com/Alee14/e8ce6306a038902df6e7a6d667544ac9

Good luck if you decide to try!

Windows acts like it is the only OS installed on the machine. Your best bet is to physically disconnect all other drives while installing windows.

It is saving you. Don't install an OS to removable media. (Especially Windows since it is I/O heavy)

Windows doesn't install to USB.

You could probably get round this by creating a VM and passing this disk through as the only storage. Do the Windows install in the VM and then delete the VM and boot directly to the disk.

If you want to dual boot, the best way to do it is with an internal drive.

For the smoothest operation, I strongly recommend using an internal drive with only Windows installed, and a separate boot drive for Linux, such as a portable hard drive. Linux Mint works particularly well in this setup.

I believe there are ways of skipping this error and installing on an external USB drive. The question is - would you really want to use Windows over USB. It would be unbearably slow.