Earth is about70 percent ocean and about 30 percent land. If the sea level is lowered enough, all the contiental shelves will be exposed, and there will be a few percent more dryland.
And then then lowering the sea level will not do much to increas the land ara, because continents will never come close to 50 percent of the surface of Earth. Musch less than 50 percent of the surface of Earth is continental rock towering about the sea beds.
It is hard to tell exactly from the maps in this comic strip, https://what-if.xkcd.com/53/ but it looks like about 50 % of the earth's surface would be dry land if the water level dropped tosme level between the three kililometer drop map and the five kilometer drop map.
That would drastically reduce the amount of water on Earth, causing extreme climate change.
I think that the more reasonable way to design an imaginary planet with about 50 percent land surface would be to have a somewhat different geology causing much more o rmuch larger continental land masses to form. With more high continents, the world could have a much water as Earth, but the oceans would be smaller and deeper. Much of the lower parts of the continents would be submerge, but the dry land would be enough for about 50 percent of the world's surface to be dry land.
Since the moving crustal plates of the Earth are forced deep underground and melted into magma at many of their junctions with other plates, and are being created at other places, I find it easy to believe Earth might have had higher or lower percentages of continental crust in the past and might have higher or lower percentage in the future. And another planet with different geology coud easily be 50 percent continental crust at some points in its hsitory while having about as much surface water as Earth.
I'm not certain that making your world an alternate univese version of Earth would work. You need a geological opinion for that. I note that water deep underground is supposed to be a lubricrant for plate techtonics, so an alternate Earth with less water might have slower moving crustal plates or no plate techtonics at all. If crustal plates move slower on your world maybe you could find a map of a past era where Earth had 50 percent of its surface contental plates instead of 30 percent. But since plates get dissolved as they plunge under other plates, I don't think there is any record of destroyed continental plates.