Medium no longer uses a custom or proprietary font for body text. They used to use Freight Text, but now they use Bitstream Charter, which is free (in several variants):
Charter is an excellent and very legible font. I wish more people would use it, especially in the LaTeX world, where most people stick with the to-my-eyes nearly unreadable default Computer Modern.
A few critiques of your design:
You put linebreaks in unexpected and jarring places, breaking the flow of paragraphs. For example, in the paragraph under the heading "The Hero".
You use a narrow column for body text. This is often recommended by typography nerds, but it doesn't play nicely with elements that can't be hyphenated and split across multiple lines, such as <code> spans. See eg. the paragraph under the heading "Content font". I suggest using a wider text column to make the resulting line-breaks less jarring relative to their surroundings. You might also want to enable "hyphens: auto" in your CSS, or use a JS hyphenation library (make sure to load it asynchronously so people on slow connections can still read your content while it's loading!).
And finally, there's more to typography than choosing typefaces, as I hope the above makes clear.
Computer Modern is indeed a poor font from the stone age of digital typography. It's the Comic Sans of computer science.
However it effectively communicates "I'm a serious expert in this computer stuff and you won't understand this text anyway", which is why blockchain ICO fraudsters write their zero-content whitepapers in Word but change the font to Computer Modern.
Computer Modern is bearable in print (although there are many better-designed options from commercial font designers if you want a good 18th century style Didone face).
The problem is that most documents set in Computer Modern are not read on paper but on screens, where its legibility is very poor due to the extreme contrast between stroke widths.
The spindly nature of Computer Modern that you see on computer screens is because of a poor translation of Knuth's Computer Modern design (whose default parameters were tuned taking into account the amount by which ink spreads on the page, on the printing devices Knuth was targeting) into outline fonts (which do not take into account the fact that there's no ink spread on the screen). See for example https://tex.stackexchange.com/a/361722/48
thank you rntz, I recognize I am at the very beginning on the road to a good knowledge of typography and how to use it well on the web. You enriched me with all those feedbacks! (:
https://practicaltypography.com/charter.html https://www.samiam.org/blog/2014-07-04.html https://ctan.org/pkg/xcharter?lang=en https://software.sil.org/charis/
Charter is an excellent and very legible font. I wish more people would use it, especially in the LaTeX world, where most people stick with the to-my-eyes nearly unreadable default Computer Modern.
A few critiques of your design:
You put linebreaks in unexpected and jarring places, breaking the flow of paragraphs. For example, in the paragraph under the heading "The Hero".
You use a narrow column for body text. This is often recommended by typography nerds, but it doesn't play nicely with elements that can't be hyphenated and split across multiple lines, such as <code> spans. See eg. the paragraph under the heading "Content font". I suggest using a wider text column to make the resulting line-breaks less jarring relative to their surroundings. You might also want to enable "hyphens: auto" in your CSS, or use a JS hyphenation library (make sure to load it asynchronously so people on slow connections can still read your content while it's loading!).
And finally, there's more to typography than choosing typefaces, as I hope the above makes clear.