Ok so there's a lot of different elements happening at once regarding game design and dev's intentions, and obviously I'm not the dev or speaking on behalf of them but just figured I put most of this into 1 post to help clear up/consolidate it for the 3 people who will read it before it gets buried and forgotten. First thing to say is that this game is designed with the intent to be replayed which is obvious by the many different endings and new game plus. Do a run, learn some things, make mistakes, play again. It is a dating sim after all and whats a sim without making mistakes?
Right now there's the base game and the DLC which adds Amy, Kat, and Reona. The dev has stated that all NTR is avoidable (the definition of avoidable is up for debate among people in this thread). To my knowledge it was never clarified if that was in regards to the base game or the game AND all its dlc. With the base game there are moments where you can stumble upon NTR without any advanced warning. Alexis is the prime example with her first event, Aletta can be fucked by Dwayne before you have sex with her or else you share Lexi with Dwayne (this is avoided by sleeping with Lexi or dealing with Dwayne before this event).
In regards to the DLC characters, Reona does hook up with someone before you are exclusive/discuss what type of relationship you have. If this is or isn't NTR is sorta moot because its unavoidable if you wish to progress with her. If you consider that NTR you wont like it, if you don't consider it NTR or are indifferent you wont care. Sadly it just becomes a definition game. Personally I don't care, its a sim and Reona is supposed to be a slut. Sluts sleep around and having her do that is realistic. That being said, yeah there's no real warning and the "NTR is avoidable" might make you think that wasn't going to happen. So in the most technical sense you can avoid NTR or NTR adjacent scenes using the wiki, or not playing the DLC but that means devaluing some of the dating sim/game elements. In the same way warnings in the game itself would devalue it.
With Kat there's a scene where if you choose not to fuck her on cam she finds some other male "talent". If you're fine with this it goes nowhere, otherwise it leads to a relationship ending event. If you're following her path doing all the normal choices you'll never run into this but its still there as a thing that can happen.
Now all this being said I like the game and I like the Dev. I'm into corruption and redheads. This game's got a lot of the former and less of the latter but I realize and accept there will be things that aren't perfectly for me. If we're all being honest the perfect solution is probably a setting to toggle warnings of "hey this path/option/character might contain things that are/might be considered NTR and if you don't like it that's fine but this isn't for you".