Hmm... It would help to know what kinds of non-anime shows they prefer. Are they into fantasy, horror, romance, drama, sci-fi, etc? I'll give more than three, but I can narrow it down to whatever their preferences may be.
For Romance, I suggest: Horimiya | My Little Monster | Kaguya-sama: Love is War | Eden of the East
(Take into account that I am female and prefer shoujo types of romance - their mileage may vary.)
For Fantasy: Inu x Boku SS | The Ancient Magus' Bride | Land of the Lustrous
For Horror: Hellsing Ultimate | The Promised Neverland | Angels of Death
For Sci-Fi: Psycho-Pass | Akudama Drive (I don't watch much sci-fi but I've heard Cyberpunk: Edgerunners is good too)
I find that introducing people through anime movies is easier than trying to get someone to watch a whole series right away, however. Definitely get them to watch the classic Ghibli movies like Spirited Away and Howl's Moving Castle. Your Name and A Silent Voice are excellent ones as well.
Also just going to throw it in here just because it's my favorite anime, but Erased. I think that one's pretty easy to digest for newcomers as well with the absence of many over-the-top anime tropes while still making for a compelling show. I'm also going to suggest Demon Slayer because, while some people really love it or really hate it, it definitely has a certain appeal to people who haven't watched much anime with the abundance of flashy animation and fight scenes.