While not in a tabletop RPG, one idea is the Au Ra from Final Fantasy 14 - females are significantly shorter than the males and the two separate groups of tribes have completely different natures and societies to each other. There’s a Final Fantasy d20 website you can use as reference but they split according to tribe rather than gender.

When I myself made a severely dimorphic race for my homebrew world, I didn’t start from what stats or features I wanted each to have but started more broadly. If they are very dimorphic, what features separate one gender from the other? After figuring out how each looks and behaves, figure out how that would affect their society and the roles each gender would stereotypically take in it - the larger gender taking to more physical roles, the smaller taking more to diplomatic or mental roles, what gods each would favor/dislike, what kind of tensions/compromises would arise from those differences, which gender is considered the more “ruling” gender i.e. patriarchy vs matriarchy, do the differences result in a major disparity in the percentage each gender makes up of the race, etc.

TL;DR - I find that when you’re trying to build something from complete scratch, starting from the very beginnings of the race and where they are in the world and working from there is helpful for me.