“The Plot Against America” actress, 48, says Gibson, 64, made “hateful” comments to late makeup artist Kevyn Aucoin over 20 years ago at a party.

“I believe in redemption and forgiveness and hope that Mr. Gibson has found a healthy way to deal with his demons, but I am not one of them,” Ryder tells The Post. “Around 1996, my friend Kevyn Aucoin and I were on the receiving end of his hateful words. It is a painful and vivid memory for me.”

Ryder also said the actor, who has been accused of anti-Semitic and homophobic words in the past, needs to come clean about his past so he can move forward.

“Only by accepting responsibility for our behavior in this life, can we make amends and truly respect each other, and I wish him well on this lifelong journey,” she adds.

In an interview with the Sunday Times, Ryder first alluded to the alleged homophobic remarks, as well as anti-Semitic comments made to her in which he allegedly called her an “oven dodger,” an offensive term for Jewish people in the Holocaust, while discussing her heritage.

“We were at a crowded party with one of my good friends,” she said. “And Mel Gibson was smoking a cigar, and we’re all talking and he said to my friend, who’s gay, ‘Oh wait, am I gonna get AIDS?’ And then something came up about Jews, and he said, ‘You’re not an oven dodger, are you?’ ”

However, reps for Gibson deny Ryder’s allegations.

“This is 100% untrue. She lied about it over a decade ago, when she talked to the press, and she’s lying about it now,” the reps said, referencing a 2010 GQ article when Ryder first mentioned the alleged incident.

Gibson, though, was canned from his role in Netflix’s highly anticipated “Chicken Run” sequel Tuesday after the remarks surfaced.

The “Braveheart” actor-director was first accused of making anti-Jewish remarks in 2006, when he was arrested for a DUI near Malibu, California, and told a police officer that “Jews are responsible for all the wars in the world” and referred to a female officer as “sugar tits.”

Aucoin, who was openly gay and awarded an honorary degree from the Harvey Milk HS for his activism, was a makeup artist to major celebrities like Madonna and Cher and supermodels including Naomi Campbell and Cindy Crawford. Despite his prolific career, Aucoin died in 2002, at age 40, after a battle with acromegaly (a pituitary disorder) and complications from prescription painkillers.