They’ve never used the word “galaxy,” feels like there could be something there. “Fate of the Galaxy” or some such (though my gut tells me there’ll be a verb in there). They’ve also never used the word “light” before, which is not surprising (since that’s kinda newish) but there’s maybe a way to work that in.
If it were me I’d probably try to mirror ROTJ/ROTS with something along the lines of “Rebirth of the Republic.”
If it’s a line from a previous movie (like TLJ), the smart money would be “Spark of Hope” (which would have the added benefit of bringing things full circle with “hope”).
“Balance of the Force” seems to be the main guess on the street, though personally I doubt they’d use the word “Force” again so soon. My actual guess is that it’s probably something people aren’t really guessing and probably something more general like TFA/ANH. I would have also guessed they’d find a way to subtly imply with the title that it’s the last movie, though TLJ already used one of those words.
Basically, who knows (especially when we know nothing about the plot).