You see that look in the movies a lot as well. I think it's just a question of taking the stays out.

I can get close with a couple of Mercer point collar shirts I own. Those collars aren't lined, which encourages the floppiness.

If I took the stays out of a modern non-iron point collar (Lands End or Jos Banks or Brooks) it would look sloppy, not floppy.

I used to regularly buy J. Press Madaralyte blue-white pencil-striped plain collar shirts with flap pockets, in the '70s and '80s, when they were Press staples, and I never used collar stays, and the floppiness of those shirt collars was unparalleled in the history of floppy Ivy tennis collars ...

the shape of those unlined collars was perfect and the lightweight pinpoint cloth also contributed a lot to the softness, which is never realized exactly the same way with an oxford cloth shirt even if it's been washed many times .....