Growing up, Jessica Keenan Wynn didn’t know much about ABBA beyond “Dancing Queen.” But, like many Americans, she became an instant fan of the Swedish pop group after seeing a production of the musical “Mamma Mia,” as a teenager. Now a 32-year-old actress, she’s starring in the follow-up to the 2008 movie adaptation.

“Have I peaked?” she asks The Post, laughing. “When your first major film is with Meryl Streep and Cher, you tend to wonder what could possibly surpass it.”

In “Mamma Mia! Here We Go Again,” in theaters Friday, Sophie (Amanda Seyfried) prepares for her hotel’s grand opening in the present day, while flashbacks reveal how her mother Donna (Lily James taking on Meryl Streep’s part) ended up on the fictional Greek island of Kalokairi. In the 1979 storyline, Wynn appears as the younger version of Christine Baranski’s posh divorcée Tanya, Donna’s close friend.

Wynn prepared for the part by re-watching some of her favorite Baranski performances, including in “The Birdcage” and the sitcom “Cybill,” to learn how the 66-year-old moved and held herself.

“When I met her,” Wynn says, “she opened up her arms, came gliding towards me, and the first thing she said was, ‘Oh, Jessica, we have the same mouth!’”

Born and raised in Los Angeles, Wynn got her start in showbiz at 6 months old on an episode of “The Golden Girls.” But talent runs in the family: Her maternal grandfather was character actor Keenan Wynn, memorable in “The Great Race” and “Dr. Strangelove,” and her great-grandfather was comedian Ed Wynn, known for classics including “Mary Poppins” and “Miracle on 34th Street.”

“It was daunting when I came to the realization of the magnitude of their talent and the influence in film and TV and radio,” says Wynn. “To be honest, I think now with ‘Mamma Mia’ coming out, a part of me finally feels like I am maybe carrying on their name and walking in their large, large footsteps.”

Now calling New York’s Upper West Side home, Wynn recently completed her third run in Broadway’s “Beautiful: The Carole King Musical” as songwriter Cynthia Weil. She had returned to the role after finishing production on “Mamma Mia,” and coming back, she says, was a strange transition.

“When I’d run into people in the hall or backstage, they’d be like, ‘How was it?’ And you just can’t really articulate it, can you?” she says. “You just go, ‘It was nice.’ You can’t say, ‘It was the greatest experience of my life and nothing will ever compare to it and I just need to be alone for a minute to kind of think it all through!’

“That wouldn’t go over too well,” she adds with a laugh.