People like to say that decades ago cars didn't look alike, but in the late '70s and early '80s cars were bricks, while later in the decade they were all jellybeans. I have come across articles from the '50s bemoaning the similarity of American cars of that era. Rinse, repeat. :-)
As much as I love '20s and '30s cars, I can't say I'd be able to ID a bunch of them, as I haven't studied all their styling cues. Does that mean they all look alike?
Are today's cars "all alike"? I'm not so sure. If you look carefully you'll note differences. As it is now, Cadillacs have had an interesting design language I don't see in other makes. Also, there's no mistaking the Lucid Air, Rivian trucks and of course the Cybertruck, for anything else on the road.
I've always wondered if the average teenager or housewife (non car fans) could ID cars of, say, the '50s.