Ok, so the Wikipedia page for the Olivetti Lettera 22 typewriter says Joan Didion used one, but my brief internet research shows these two photos, where she has some model of Royal (anyone, typewriter nerds?) and a Hermes Ambassador.
#Typewriter #JoanDidion
The Eggers interview (which i think i found a review saying it mentioned the Lettera 22) mentions the Thinkpad, but not the Lettera 22. Salon, 1996, https://www.salon.com/1996/10/28/interview_11/ [edit: the source of that memory is this article https://www.millersbookreview.com/p/writerly-life-joan-didion which mentions the Lettera 22, but not in connection with Eggers, and with no other source]
The Salon Interview: Joan Didion - Salon.com

Salon.com

Evelyn McDonnell mentions, without source, a Lettera 22 and a Royal 200. https://lithub.com/to-be-a-writer-you-must-write-how-joan-didion-became-joan-didion/

Specifically, the Lettera 22 is used for retyping Ernest Hemingway stories.
[edit: references Paris Review and Ms magazine interviews; https://achievement.org/achiever/joan-didion/#interview mentions typing out Hemingway, but not specifically the typewriter]

“To Be A Writer, You Must Write”: How Joan Didion Became Joan Didion

Joan Didion looks straight at the camera, with her fist curled in front of her mouth—as if to indicate it is through her hands that the taciturn thinker speaks. Appropriately, a manual typewriter t…

Literary Hub
Another lithub article https://lithub.com/how-the-barbizon-gave-sylvia-plath-and-joan-didion-freedom-and-creative-autonomy/ mentions Joan Didion flying in 1955 [edit: oops] (her first flight) with an Olivetti portable with travel case, and in passing implies that this is the sort of item that a New York debutante literatum would seek. The Lettera 22 is launched in 1950 (or possible 1949) and would fit the description. Joan "turned up at Berkeley" [presumably in 1953, being a Junior when she's flying] with the Olivetti portable.
How the Barbizon Gave Sylvia Plath and Joan Didion Freedom and Creative Autonomy

Joan Didion, who would become known as one of the finest writers and chroniclers of America’s political and cultural shifts, checked in to the Barbizon in 1955. She arrived, just like Sylvia Plath …

Literary Hub
The _later_ Paris Review interview is in 2006 https://www.theparisreview.org/interviews/5601/the-art-of-nonfiction-no-1-joan-didion and does not mention a typewriter. Weak sauce.
The earlier Paris Review interview is in 1978 https://www.theparisreview.org/interviews/3439/the-art-of-fiction-no-71-joan-didion and specifically mentions typing out the Hemingway, but does not mention the typewriter model. (though typing at 15 or 16, the Lettera 22 would have recently been made available)
The Art of Nonfiction No. 1

  The last time this magazine spoke with Joan Didion, in August of 1977, she was living in California and had just published her third novel, A Book of Common Prayer. Didion was forty-two years old and well-known not only for her fiction but also for her work in magazines—reviews, r...

The Paris Review
@drj It's a Royal KMG made from '49-52 and many of the design elements were done by Henry Dreyfuss who redesigned the Quiet De Luxe at the same time. I've got a couple of them: https://boffosocko.com/tag/royal-kmg/
Royal KMG | Chris Aldrich