This is a loosely structured "tutorial" (but really only useful if you know what you're doing) for installing Windows 10 on MacBookAir4,2
(but will probably work on other relatively old models as well), because all other methods hanged the machine at some point (including OpenCore) and I haven't seen it described elsewhere.
The MacBook's internal drive broke down and I needed to install Windows after replacing it, preferably without having to install macOS first just to remove it later -- I don't have much disk space to lose.
I have verified that this instruction works for tiny10, so that's good, and the default Windows 10 build probably works as well, but I prefered something lightweight, so that's what I went with.
My main machine runs Linux, but you can probably repeat the same instructions under Windows. I didn't want to install Windows twice so I found Linux tool replacements for everything I need