Several things show up when I check my favorites for this, but most of them are tanks where NTR is a one-off in a single chapter of a standalone story, so I didn't read them anyways. As for the results I go that are individual manga and doujinshi, most are not what anons would consider NTR.
A shota is cucked, by bugs, but it's the 4th in a series that was about bugs turning lolis into broodmothers where there wasn't cuckoldry before, and it end with him burning everything down.
A Literal Skyrim NPC gets cucked during the PC adventures Mod Land. They're not human, they have no souls, they're all objects.
Guy's mom turns out to be a porn star and he fucks her. It was ongoing last I checked, so I'm not sure if newly added chapters added NTR, but if not, I assume the "NTR" is just him seeing his mom getting fucked in the first place, which is the impetus for him to begin fucking her.
It says NTR, but the tag is weak and it's 95% tentacle porn, so I assume it's just because she had a boyfriend or something before getting space raped.
Guy mind controls lolis. Supposedly thye have some canon love interest that he pretending to be. Don't know the show and don't care. Don't like mind control either. I like the style. Too bad about the censorship.
Too long and can't remember, but the NTR tag on this one is weak.
Another weak NTR tag, presumably because Shierke likes Guts and was mindfucked by him in the last chapter. This is styled as a comical parody though, so nothing that happens is serious. The last chapter had Guts cutting Griffith and Zodd in half with his penis.
Pic related. The one NTR that even some anti-NTR anons, given they are homosexual, think is an exception. Man is NTR'd by twink faggot pretending to be a woman. Man takes back his wife and
fucks the twink faggot. And they all live happily ever after.