Super late but I just made this list and sent this to a creator I know. I stumbled upon your by accident while searching for inspiration myself.
Top-Tier NTR Potential
Naruto
Sword Art Online
Dress-Up Darling
Frieren (Both Frieren and Fern work as a focus.)
Komi Can’t Communicate
Re:Zero
Your Lie in April
The Angel Next Door Spoils Me Rotten
Okay Potential
Spy x Family
Kaguya-sama: Love is War
The Quintessential Quintuplets
Chainsaw Man
SNAFU
Konosuba
Highschool DxD
To Love Ru
Bleach
Mushoku Tensei
Apothecary Diaries
Danmachi
My Happy Family
Spice & Wolf
Would Be Great but Often Overlooked
Kimi ni Todoke
Maid Sama
Fruits Basket
(Pretty much any classic shoujo romance)
The best NTR setups focus on a single pure, devoted heroine and a flawed MC—someone absent, shy, or neglectful—making the betrayal more personal and painful. The heroine should also have flaws: shy, inexperienced, pure-hearted, easily manipulated, or emotionally vulnerable (lonely, frustrated, or naive). Harem and comedic series can work but are usually too spread out or lighthearted to hit as hard. In some cases one of the characters just doesn’t fit well—like the MC from My Happy Family, who’s too present and not clueless—but it’s still decent overall.