I'm trying to create an Option for profiencies for my homebrew race, using Tabaxi as a base. ("You can choose two proficiencies out of the Intimidation, Investigation, Nature, Perception, and Survival skills.") I've created the Option itself, but when I scroll down inside the Option editor and expand the Modifiers section, the button to Add Modifier just isn't there. I've finished everything else with this race and it's working perfectly, but this one last thing just won't do what it's supposed to.

You are probably doing this in a phone or tablet? Turn it sideways to make the display wider.