Do we know that prime Sulu is straight? He flirts with a woman in “The Way to Eden” and when the literal devil from Christen mythology is aboard the Enterprise in “The Magiks of Megas-Tu” Sulu is able to conjure a woman using the magical properties.
Mirror Sulu clearly is interested in Uhura, despite her rebuffs.
And we do see Kelvin Sulu ever so briefly with his husband and child in “Beyond”, causing an uproar well out of proportion to how little the movie choose to show.
However, all those characters might be bisexual. We do exist.
Even while it was still on the air, I assumed Prime Kira was closeted and that was part of why none of her relationships worked out.
People have relationships that don’t work out without being queer.
But yeah, prime Kira is a religious conservative who is grossed out by how libertine Dax is – dating Ferengi, and dudes with transparent skulls – and while we’re never told how Bajorans view queer relationships, I do view mirror Kira’s more unrestrained nature as indication that her prime counterpart is holding back a part of herself.