In incez game where the mom supposed to be MC lover, it is.
If it's not incez game, then it's not NTR.
Even in an incest game, you realize your mom had sex before, right? The MC isn't the son of god. If the game has a scene at the very start of the game of the mom having sex with the dad, it's not NTR. In fact, plenty of games use that as a way to make the MC start to have those naughty feelings.
So not only is the scene avoidable, when it happens she isn't an LI yet. The MC has no feelings or intentions towards her at that point. That comes later in the story. So technically, it's not NTR.
In fact, none of the scenes are.
Watching the couple having sex in their home is voyeurism, because she's not an LI nor do you ever have any sex scenes with her.
The futa scenes, besides being optional, are sharing.
And the ghost scene is also sharing.
Now, you might not like sharing and that's fair. But technically there's no NTR. And I say this as someone that heavily dislikes NTR. But I haven't had an issue with this game despite this (even though I would have liked to have the option to skip the sharing scene).