I agree that OD&D is very S&S {snip}
I wanted to address this further when I had the chance, which I do now. This specific topic came up before when discussing the Greyhawk setting. Here's the (very) lengthy thread starter:

D&D General - For the Love of Greyhawk: Why People Still Fight to Preserve Greyhawk
On the recent thread regarding the upcoming hardcover book and a discussion regarding Iggwilv and Tasha- https://www.enworld.org/threads/iggwilv-tasha-to-join-volo-xanathar-and-mordenkainen-updated.674231/ .... a discussion broke out about Greyhawk, and canon, and what is good, and bad, so on...

There was a brief companion thread later about genres and campaign settings (more on Eberron as noir) here:

D&D General - Genres and Campaign Settings, and why D&D is not a Work of Literature
Moving somewhat tangentially from the previous 3,804 threads on Greyhawk (numbers are approximate), I thought I'd go more deeply into a discussion about why there is a limit to analogies regarding campaign settings and genre. While this topic originally came up regarding Greyhawk and "Swords and...

Getting to the original topic, there are those (such as me) who might describe the original, 1983 and prior, Greyhawk setting as S&S.
On the other hand, there are those who might observe that D&D itself, in 1983 and prior to that, was more S&S, therefore the default setting wasn't necessarily S&S in and of itself, so much as it was a conduit for the default playstyle, which was more S&S-influenced.
Which brings up the natural questions- what, about early D&D (OD&D, early AD&D, Moldvay) is S&S? I would put forth that the following factors combined in various ways to make it feel more S&S, in terms of providing a better definition of the term specifically for the TTRPG genre (with the assumption that "Early OD&D mimicked S&S"). One factor that is also lurking within the background is that the people playing back then were necessarily more influenced by the writers of the S&S genre, since they were more current and well-known at that time than they are now.
1. Danger. Look, it's not like Conan or Fafhrd or the Gray Mouser or Elric were getting killed off in every short story (let me introduce you to Conan II!). But early D&D was certainly dangerous- whether in terms of traps, death, TPKs, or any number of other factors. While this mapping to the literary genre is inexact, there was a real feeling of danger to the characters, because the world was dangerous, and the characters could (and would) die.
2. Good doesn't necessarily triumph. This is not Tolkien or Lloyd Alexander; the heroes are not destined to do great things, and good does not win out. Sometimes evil triumphs. In the long run, maybe it's inevitable.
3. Complex and gritty. Look, it's a fantasy world, but it's a fantasy world that's out to get you. Civilization exists in patches, and where it does exist, it's not always a great thing; great power corrupts, and great kingdoms (or, in the case of Greyhawk, the Great Kingdom) are likely to be corrupt and fallen. A thieves' guild is likely to be the real power, if not the Mayor.
4. Low magic. This is a rather ... we'll say arguable topic, as people love to discuss what defines low magic. But in early D&D, there were no cantrips, and magic users were notoriously underpowered for many levels; you could and would have multiple combats go by without any spellcasting. Because spellcasting took a while, and due to initiative, the ability of martial characters in your party to "disrupt" evil spellcasters was always present, giving some verisimilitude to the S&S trope of the swordsman who has to close in with the sorcerer.
5. Ye olde inne. Look, it's a hoary trope now, but the concept of a group of mercenaries looking to be hired for a job ... that's as S&S as you get. There are no grand adventure paths- just jobs to be done, tombs to be raided, and, um, modules to do.

6. Characters are selfish. I don't want to put too much of an emphasis on this- the PCs will have other interests and other goals, but when we discuss S&S, the characters aren't saving the kingdom because it's the right thing to do- they do it because they are paid (and, often, double-crossed). In early D&D, this is reflected by the emphasis on money as XP.