OK, yes, but that is over simplifying Einstein’s “thought experiment.” Or perhaps he’s the one who oversimplified it?

He should have said there is no experiment which can distinguish between an acceleration and a uniform gravitational field.

Of course, the latter doesn’t exist in nature. So,…

I posed a similar question to one of my physics professors. His answer was that an idealized version of the experiment would not compare an accelerating spaceship with the Earth, but would compare an accelerating spaceship with an “infinite plane (or slab) of uniform mass density”.