How does Renato D'Agostin achieve these super minimalist and high-contrast photos?

Upon viewing his portfolio at the link you provided, my first thought was push processing. In push processing, one typically underexposes the shot (that is, meters and set exposure as if the the film were a higher ISO than it really is), then compensate in the darkroom by overdeveloping the film to account for the underexposed shot.

Push processing tends to increase the contrast of the photo, as well as increase the film grain, making it appear very grainy or "noisy". Renato's portfolio certainly shows this.

D'Agostin appears to do all of his work in the darkroom, rather than scanning film and editing in post/Photoshop. For instance, in this interview with D'Agostin by bestkeptsecretsintheworld.com, Renato says (emphasis mine),

Actually, I quit after two months the Photography-school in Milano. It was not for me, so I started to be Photographers Assistant where I spend a lot of time in the darkroom.

Your work is still analogue and hand-printed black & white Photography with lots of grains in it. Which camera and film do you use?

A Leica M6, which is very small and easy to carry around. Film, basically everything I can find, but I prefer Kodak Tri-X400.

[re: digital photography,]

No, I’m not interested in Digital photography. I can’t stay behind a computer for many hours. It’s not natural for me. I want to use my time and skills in what I love doing.

In this 2017 interview with MAPS-mag.com, he clearly indicates his preference for film and darkroom processing (emphasis also mine):

Which film do you prefer to take b/w photo?

I mostly use Kodak Tri-x 400. Sometimes Ilford 3200, it depends on the project. And sometimes whatever I find. I’m not very technical, as I believe in the photographic result rather than the way I got there or what I’ve used.

Do you print film by yourself?

I process film by myself, and then print the photographs in my darkroom, which has become an essential part of my life.

What is the most important for you?

My lonely moment in the darkroom thinking about what my photography is and what I want it to be.

D'Agostin's images are certainly stylized for, and emphasize the results of, push processing. He also prints very large – I saw somewhere he moved to a studio darkroom where he could print at over 2 meters, from 35mm film — which would also overemphasize film grain when viewed at typical poster print size viewing distances. So that's certainly his style, especially in conjunction with his use of uncluttered subject framing and long-focal-length lens to isolate the subject from its environment.

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With regards to emulating his style using your DSLR, realize that the digital "equivalent" of the darkroom is Photoshop (or its alternatives). To the extent that you're trying to copy his style, your camera settings don't really matter that much. That is, you have a lot of leeway to lose image information – increasing contrast, adding grain, converting to B&W, etc. – from an otherwise well-exposed image. His darkroom style lends itself to relatively easy emulation in Photoshop, turning digital captures that might be suboptimally exposed into D'Agostin-esque art in the digital darkroom.

I don't mean to belittle his style — I quite like his portfolio. And judging from the esteemed galleries that show his art, it seems to be well-regarding. But with regards to emulating the style digitally, it's a very forgiving process in post-processing, not requiring a lot of technique in the capture per se. (Notwithstanding the art of composition, regardless).

With selective grade contrast papers and a variety of film processes you can achieve these results. I don't know if there's negative combinations or pre-flashing of the paper, but all of these are easily achieved in the darkroom after a couple of weeks of practice.

I hate to say it but these appear to be pretty simple- so the fact that they're interesting says I'm missing something in the presentation.

Edit: I went and dug out this OLD web photo. It's a scan of a print, and it's from 1993. The print's paper is black- pitch, pitch black. It was printed on a selective contrast paper (Kodak RC) with a #5 filter. The filter (deep magenta) selective exposes the high speed grains in the paper, which gives it more contrast relative to the original image. The original photo was taken at night, hand held, with a f1.4 and a Canon camera. The film was Kodak TMZ3200, pushed to ISO 12800 and probably still underexposed. The subject was a man who had just crawled out of a cave to get help for his friends which were stuck 3 miles in... with rising water. The face was lightly dodged with a custom cut mask to prevent total blocking.

I've provided the photo (even tho the black isn't black in it... sheesh scanned nearly 25 years ago), just to give you an idea of what's rapidly and easily possible in a 'wet' darkroom. I'd encourage you to read some books on photography, and if you want to go all-in read Ansel Adam's series on camera, negative, and print.

Another option is to shoot through colored filters. Back in my "I'm going to be a real photographer!" phase (before I realized I had absolutely no talent for it), I shot a lot of B&W through various filters to enhance or reduce contrast. Red filters darken blues (making white clouds stand out against a blue sky), green filters darken oranges (bringing out freckles on pale skin), etc.

I haven't tried it since I went digital, so I don't know how well it would work, but you could try to shoot through a colored filter, then desaturate the resulting image in PS or gimp. You won't get the lovely grain effect¹, but the results may be interesting.

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1. TX400 4 LIFE!

View this Leica blog and look at his negatives. He used a lot of TriX 400. The idea is exposing for the right things. He exposes so that the shadows are all dark. You can certainly bring the highlights up in post processing, but look for high contrast light - noon light and shadows. https://www.leica-camera.blog/2015/08/12/renato-dagostin-coast-to-coast-at-mile-1882/