@phaer Oh I should've linked the docs instead, that's my bad. Here it is: https://search.nüschtos.de/?scope=NixOS&option_scope=11&query=boot.loader.systemd-boot.windows&option=boot.loader.systemd-boot.windows.%3Cname%3E.efiDeviceHandle

TL;DR, yes you need a EFI shell.