Is the term “donor” appropriate to refer to a machine used for parts? [closed]

Yes, that is perfectly normal usage across wide areas of the US.

A donor car is effectively a vehicle that is bought to plunder for parts to use towards a kit car project. Depending on what parts are included with the kit, important parts such as the engine, running gear and chassis may be needed, as well as smaller detailing parts such as trim, brightwork, interior and wheels.

https://www.google.com/search?q=%22donor+car%22&rlz=1C1CHBF_enUS724US727&oq=%22donor+car%22&aqs=chrome..69i57j0i512l9.13083j0j7&sourceid=chrome&ie=UTF-8

I would add that is normally used in the context of a specific project. And it normally means there are several parts or a major assembly to be pilfered.

An electronics example "donor computer" - https://www.youtube.com/watch?v=O9RJ_RK9WQ4