Unlike "raw" images, a QCOW2 file only takes up space on your physical drive for the data actually written inside the VM.
qemu-system-aarch64 \ -M virt -cpu max -m 4G \ -bios QEMU_EFI.fd \ -drive file=win10arm.qcow2,format=qcow2,if=none,id=hd0 \ -device virtio-blk-device,drive=hd0 \ -drive file=win10arm64.iso,format=raw,if=none,id=cd0 \ -device virtio-blk-device,drive=cd0 \ -netdev user,id=net0 -device virtio-net-device,netdev=net0 \ -device usb-kbd -device usb-mouse \ -device ramfb -vga none windows 10 arm qcow2
Some sources offer Windows 10 ARM64 QCOW2 images, but these are often: Unlike "raw" images, a QCOW2 file only takes