That depended on the society. The final result was a combination of both the infanticide and what might happen to older/adult people, as things like warfare could kill off a lot of men bringing the adult sex ratio closer to 1:1 (or in some cases, when most or all of the men of a group were killed off, it could go the other way).
Among the polyandrous Inuit/Aleut the sex ratio about about 2:1 male, but that’s because marriages were assumed to be two men and one woman. This was enforced by infanticide.
In the islands of the Pacific, infanticide was a means of population control on very limited islands. Infanticide in general was one way to limit population, but a number of island cultures were specific in limited female infant survival. Excess male population might be taken care of by warfare with other groups. Excess population in general could be solved by piling people into a canoe and sending them off to find another island.
In Ancient Greece and Rome infanticide was used to eliminate deformed children as well as unwanted children. Some of them were rescued and became slaves but others weren’t. The upper class Romans had a lot of families with multiple sons and only one daughter, which leads to the question of why only one girl? Well, there’s your explanation. I think that was connected at least in part with their dowry system.
Some cultures forbade infanticide, such as the Ancient Egyptians, who were considered weird for keeping all infants by the Greeks and Romans.
Some cultures that were smaller than the ancient empires, and who were at war a lot, had the opposite problem: so many men killed by violence they had surplus women. They wouldn’t want to kill off female infants because of the need to replenish their numbers, and they wouldn’t kill off young boys because of the need for warriors. So you often would see polygyny in such places and there wasn’t an issue with the skewed sex ratios.
Some modern cultures that allow polygyny do have to deal with “surplus” males. This is a problem in groups like the polygynous Mormon splinters who don’t limit births and advocate each man having multiple wives. There aren’t enough women to go around and they don’t engage in warfare so “excess” boys are simply abandoned in their teens along highways, the so-called “Lost Boys”.
There are quite a few cultures that will specifically kill off infant girls. There are others who will kill off both boys and girls. I don’t know of any that will selectively kill off boys.