This has been the story of my life. I think there is a certain type of person - physical attractiveness is part of it, but charisma is even bigger – who can "get away with" flirting in unsanctioned spaces. It's a combination of being confident enough to break taboo, perceptive enough to read subtle interest cues, and being attractive enough for those interest cues to be non-zero.
I've tried to be that person from time to time, but it almost always breaks down on one of those axes, thus consigning most of my dating efforts to the soul-crushing grind of dating sites/apps.