Gnome Boxes, why does the Next button not appear when creating a VM?

I've used VirtualBox in the past, but I'm trying to migrate to Linux-native applications as much as possible. My host system is running Ubuntu 21.10, and I have installed Gnome Boxes 40.3.

I want to add a Windows 10 guest VM. I have my Win10 USB stick, and I have created an ISO from it two different ways while trying to solve my problem.

Using Gnome Disks, I can create a partition image from my Win10 USB stick. Gnome Disks wanted to add the .IMG extension to the file it creates instead of .ISO. I manually changed this to .ISO. When I had problems (see next paragraph), I wondered whether it was a result of how I created the file. So I also went to the Terminal and created a partition image with an .ISO extension using the dd command.

Unfortunately, neither of these files get Gnome Boxes to behave. On starting Boxes, I click the Plus symbol to create a new VM. Under Select an OS Source, I choose Operating System Image file. No matter which of the two ISO files I choose at the file selector dialog, I get returned to the Create a Virtual Machine page. No error message is shown. According to the Gnome Boxes documentation, after I select an OS to install, I'm supposed to see a Next button. I don't see it. I can only try again, or click Cancel.

Any advice is appreciated, thanks!

Edit: I've looked back at VirtualBox since posting this. I realized that I've never installed a guest OS from an ISO or thumb drive, only a DVD. I am wondering if there are some limitations that arise from that choice. At 15.5 GB, it's impossible to fit the Windows 10 ISO on a DVD, so that option is out for me.

Answering my own question -- but I have to credit ChanganAuto for leading me to the answer (see the comments above). An official Win10 ISO downloaded from Microsoft works fine in Gnome Boxes. Details follow.

I was reluctant to try a download since the ISOs I had created from my Win10 USB stick (using two different Linux utilities, Gnome Disks and dd from the terminal) were both 15.5 GB in size.

The official Win10 ISO was clearly different, in that it was only 5.5 GB, perhaps because I selected a single language when downloading and the USB stick has multi-language support. Still, it took me close to 24 hours to download it, I got Network Error crashes twice, and the download did not resume where it had left off. I don't know whether that problem was Microsoft's or mine.

When I selected this ISO in Boxes, I installed a VM as I expected.

Zero points to Boxes for the way that it handled what are apparently corrupt ISO files. No error dialog is shown. Some user feedback would be very helpful here. Instead, Boxes just circles you back to the Create page, and expects you to understand that there is a problem.

I also have to wonder why the Linux ISO creation tools failed to create a correct ISO from my Win10 USB stick.