Itch does not have a category of: "2d games that use 3d rendered images". You wish the site would, though. And you wish there were a category for games that are "3d". Understandable wishes, but it it is arrogant to think all those devs and a site with near 900k games are wrong in their tagging and you know a better way.
Since you mention context, context does include the site you are on.
You assume that the 3dcg tag is used to prevent misleading, because the games could be confused by their screenshots for actual third or first person games in a 3d engine like Unreal.
Those sites have few categories and the games are sorted by very few people. They would tag those games that way, even without screenshots.
Oh and Steam does have a 3d tag. It was mentioned in this very thread.
According to your own logic you are now a proven liar. (Actually, you are just ignorant)
Next, why is there no 3DCG tag there? Yes, because there is no 3D tag? And therefore there is no confusion where there are three dimensions and where there are not. Do you understand no? On sites where there is a 3D tag, pre-rendered pictures and videos, and 3D games are marked with it. But since 2D games with 3DCG pre-rendered images became popular, many sites have introduced the 3DCG tag to differentiate these games from 3D games.
Where there was no 3D tag, the 3DCG tag is also not needed
https://store.steampowered.com/search/?tags=4191
You hurl insults yet know little about the topic.
"do you understand what nonsense I wrote?" (sic)
No. I do not. My guess is, that you are looking for adult games, browsed some "blogs" that use a labeling system by putting games into categories, and those categories that interested you most were named 3d but not 3dcg. After seeing this you assumed this is the way to do this. And when you discovered itch you were confused that you could not use the known tags here, despite itch featuring "tags". But your previous encounter with tags is an observation about a limited and biased sample size. It does not hold true for things outside that bubble. And your bubble is heavily geared towards adult games. The proof is, that all the hundreds games here on itch that do use the 3dcg tag are adult games. This alone is the strongest indicator, that all you talk about here is adult gaming subculture.
And there are very few real 3d games in the adult sector. I told you how to find some of them. You can add unreal-engine to the tags to look out for. Also, you might want to try a modded Skyrim.
Oh, and what kinda bothers me, if you browse on Steam for adult games and believe that Steam does not have a 3d tag, but insist that 3d is the correct tag for that type of game ... how did you previously find 3d games on Steam? And why can't you use the same method on itch? The usual tags like walking-simulator, third-person, first-person are also used here, and some more, relating to the engine used. If a game is made in unreal-engine, I would not assume it to be a visual novel.