Yes, for some definition of OS. It could build a DOS-like or other TUI, or a list of installed apps that you pick from. Devices are built on specifications, so that's all possible. System API it could define and refine as it goes. General utilities like file management are basically a list of objects with actions attached. And so on... the more that is rigidly specified, the better it will do.

It'll fail miserably at making it human-friendly though, and attempt to pilfer existing popular designs. If it builds a GUI, it's be a horrible mashup of Windows 7/8/10/11, various versions of OSX / MacOS, iOS, and Android. It won't 'get' the difference between desktop, laptop, mobile, or tablet. It might apply HIG rules, but that would end up with a clone at best.

In short, it would most likely make something technically passable but nightmareish to use.