OK. Let me make this as simple for you as I can:
Step one: grab a Windows 11 image from Microsoft.
step two: get Rufus:
step three: grab a USB drive that will work in your Mac Pro and plug it in to where Rufus is.
step four: run Rufus and select your image.
at this point, all the bypass flags you need should be set.
step five: hit start down at the bottom of the Rufus window, and wait patiently.
Rufus will let you know when the drive is ready. Plug the completed stick into your Mac and perform an upgrade as you would normally.
while we're at it, you might wanna make sure you have the latest Boot Camp drivers available for your unit. Copy those onto your installer.
when you finish upgrading, go ahead and run the Boot Camp installer again. This will take care of any missing bits that may not have made it through.
good luck,
Nate