I know what you mean, I’ve put him in a breeder cage with a flock of females. Will keep an eye out to see if he does any male stuff lol.Do you have time to just sit and watch this bird and how it interacts with the others? That would probably be your best bet, especially if you have known females. Does it try to mount them or otherwise behave like a male?
My guess is male based on the chest, but the golden ones can be tricky. I sorted a female into the bachelor pen based on the chest once, she was pretty beat up by the time I realized my mistake but she healed ok.