CrystalFetch

Downloads official Windows images from Microsoft’s UUP servers and assembles an ISO, including ARM64.

Homebrew cask Mac App Store Direct download

What it does

Microsoft does not publish Windows-on-ARM ISOs the way it does x86 ones. CrystalFetch talks to the UUP (Unified Update Platform) servers, fetches the official packages for a chosen build, edition and language, and assembles them into a bootable ISO locally.

That is what makes a Windows 11 ARM64 guest in UTM straightforward — the two apps come from the same developer and are designed to be used together.

Notes

Everything downloaded comes from Microsoft’s own servers; CrystalFetch only assembles it.
Assembly needs several tens of gigabytes of free space during the process.
A Windows licence is still required to activate the result.

Alternative to

Alternative	Type	Trade-off
UUP dump	Free	The website CrystalFetch drives; the same files, assembled by hand
Microsoft’s Media Creation Tool	Free	Official, but Windows-only and x86-only
Mist	Open source	The equivalent tool for macOS installers rather than Windows