News Microsoft releases official Windows 11 ISO for Arm devices — Extending support for Qualcomm's Snapdragon X Elite processors

Windows relies on ACPI and UEFI (more or less what a modern PC is) for installation.

From what I understand the RPie use uboot and device tree instead of the above so it lacks what most PC users would think of as a bios.

There are various projects on github that allow you to flash a ACPI/UEFI firmware to the Pie 4 and 5 and boot Windows Arm but drivers are complicated and some will never be supported unless written specifically for Windows.

It's only a matter of time before Mediatek or Rockchip start putting out low cost Arm Mini PC's with ACPI/UEFI support.