[Arnavion]

Yes, there is a public stable API for Windows drivers. Even the built-in drivers are dynamically loaded.

Windows on ARM isn't new. The oldest Windows on ARM was Windows 8 RT (ARM32 only, I believe). Right now it seems Windows 10 and Windows 11 have ARM64 versions, but there was also Windows IoT Core from the Windows IoT OS branch a few years ago.

[oneplane]

Windows CE on ARM and Windows PocketPC on ARM is older than that. But all of it has the same issue: you nearly always need a specific rebuild for a different ARM-machine because there isn't a single "ARM PC". Just like x86 pre-ACPI where you need different HALs and bringups for different systems. The problem here is twofold: firstly windows is closed so you can't actually add/modify components and rebuild it, only binary hacks and additive installation (like driver packages). Second issue: licensing. ARM isn't available unless you are an OEM. So there is no legal way to run Windows on M1 unless you are Apple and Microsoft signs you a contract (and that hasn't happened either).

[Arnavion]

Haha, yes, I completely forgot about PocketPC.