The 20-year-old became the first Japanese player to win a Grand Slam when she beat the American 6-2 6-4.
But the final at Flushing Meadows was overshadowed when Williams called umpire Carlos Ramos a “thief” and later accused him of sexism.
“There’s a lot of stuff I want to say about how I felt,” said Osaka.
“For me, I don’t know, I don’t know, the memory of the US Open is a little bit bittersweet.”
World number six Osaka has always refused to point the finger at 23-time Grand Slam champion Williams, 37, but said she had immediately wanted to “move on” following her win in New York.
“Right after, the day after, I really didn’t want to think about it because it wasn’t necessarily the happiest memory for me,” she said. “I just sort of wanted to move on at that point.
“Of course I’m happy that I won a Grand Slam, I don’t think there’s anything that can take away from that, but I feel like it was so strange, I didn’t just want to think about it.
“I wanted to just push it to the side.”