If anything, it sounds like the unattended install file was not processed correctly. My apologies for the late reply, but I've been busy in real life. Be that as it may, we're going to have to try a different approach. What you need to do first is to undo Boot Camp and let's start again from the very top. You'll be asked to create the partition you need to place Windows upon it. Remember the size value of that partition. Walk through the wizard until you get to the point where you get the error about the install file. Before you restart, go ahead and insert a USB stick with Windows 10 build 1909 or later on it.
next, reboot the machine while holding down the option key. If you see your USB drive, select the USB icon labeled "Windows". Now, click the upward pointing arrow beneath it, and quickly press a key. Windows should start directly from the USB stick, and let me tell you, it's a lot easier if that flash drive has some kind of light on it that indicates it being accessed.
if you are successfully booting from the USB drive, you should see the Windows 10 setup screen with a language and keyboard selection. Go ahead and click Next on this screen. This takes you to another purple screen with an install button. Click it. You'll be asked to accept the legal paperwork next. Read through it if you want, but you'll have to check the box below.
The following screen is the partition screen, and you're going to see a bunch of partitions on the system. The one you want is called Boot Camp. Give it a click and then select the "drive options" button below that. With the highlight still on Boot Camp, select the button labeled format. While this will erase the label, it also converts that partition to the Windows file system. Once it's done, hit next, and it should proceed. You'll have to wait a bit if you got this far. If all goes well, Windows will be able to load. At some point, you'll be asked for a product key. You can ignore this for a bit, but you may have to select the edition of Windows that you have as well.
Since you don't have Internet yet (because you don't have any drivers), you may be able to get around the Microsoft account requirement. Do so if you are able. This makes what's called a local account. Proceed as usual.
once you get the desktop, the next big step is to go back to macOS and have Boot Camp assistant download the drivers to a separate flash drive. It's one of the options in the top menu.
when you have your drivers, go back to windows, plug, the flash drive in, and go to it in file explorer. Next, run the Boot Camp setup file and follow the instructions on the screen. Restart as needed, holding down the option key if you want to get back to windows. This time, though, there should be a hard drive labeled windows. If everything has proceeded according to plan, you should have the full support of your Mac hardware.
good luck,
Nate
