The London-born actress, whose awards cabinet boasts a Tony, Grammy, and an Emmy, revealed her bisexuality as part of British Vogue's August Pride issue.
Previously, she had shared that she was queer, and talking to writer Jacqueline Woodson, Cynthia explained why now was the right time for her to be open.
"I could feel myself actively hiding that part of myself, and it didn't feel good," she revealed. "That takes a lot of energy to uphold, and there is zero return. I felt like I was looking at my community be alive and vibrant from inside a glass box. I don't want to watch from inside that glass box anymore… There's not enough room in there, and there is no ventilation!"
Cynthia is one of 12 stars to front the glossy's August 2022 cover, joining the likes of Cara Delevingne, model Jordan Barrett, and West Side Story star Ariana DeBose.
Asked what it means to be a queer woman of colour, she said it's about "taking a risk to claim the freedom of being one's full self."
"The consequence is that some young Black queer actress somewhere will know coming in that she's not alone," she added.
Cynthia also explained that her queerness has never been a secret to her closest friends.
"I feel like I knew it when I was around 15 but didn't know what to call it," the 35-year-old explained. "I didn't have the vocabulary for it. I knew I was attracted to both men and women. I was attracted to people. I'd have a crush on this person or that person but didn't know how to put it in words."