It was this time last year that Microsoft announced that it was bringing Ubuntu to the Windows Store (now the Microsoft Store), along with other Linux distributions. If you check out the app in the Store now though, you'll find that it only works on x64 devices, meaning that you can't run it on any of the new Windows 10 on ARM PCs.
That's all about to change though. In a session at Microsoft's Build 2018 developer conference today called Windows 10 on ARM for Developers, the company showed off Ubuntu running on an ARM PC, with the app coming from the Microsoft Store. It will finally support ARM64 PCs, although x86 devices are still out of luck.
The news coincides with the release of an ARM64 SDK, which was previously never available, despite various 64-bit ARM Windows 10 devices. Presumably, other Linux distributions that are available in the Store will follow suit by recompiling their own Windows Subsystem for Linux shells for ARM PCs.
Ubuntu in the Microsoft Store still shows as only supporting x64, but the ARM64 variant of it should be available soon. You'll be able to find it here.