btw, just to start shit with the encyclopedia, but technically the "first gay kiss" in ST falls to DS9: Rejoined, which is S4, not the depicted S7 episode with Ezri. :'D
Though I'm sure trekkies would argue that that was a matter of host difficulties, but that doesn't change that it's a same sex exchange.
This is what happens when you watch The Orville, people! :P
I kind of don't care about the first gay kiss in Trek.
The Kirk/Uhura kiss was a landmark because it was the first Black/White kiss on TV. Not the first one on Trek, but the first one anywhere.
"Rejoined" in DS9 had the first gay kiss in Trek, in 1995 (if it even counts, because stomach-worms, and doesn't need to be delayed to 1998), but
LA Law beat liberal utopia Star Trek to the punch by four (or maybe seven) years, with TV's first gay kiss in 1991.
In 1990, Star Trek was afraid to confirm the existence of gays (Whoopi Goldberg wanted to ad-lib and make a line casually gender neutral, while two possible gays could be observed in the background, and someone freaked out and called the producers down to put an end to all the gayness).
Being the first gay kiss in Trek feels like a sad bar to clear.
What "first kiss" is Orville going to do on their show?
It would have to be something that hasn't happened on TV yet. I'm sure Seth MacFarlane is up to the challenge of figuring out what that line is, and then crossing it.