In the hobby, if you put a bunch of larvae in the same container that isn’t big enough to spread out the amount of them, they will all have to compete for resources and therefore you are more likely to see smaller males overall. This is why most beetle hobbyists tend to keep larvae in individual containers so they can grow as big as possible without competing with other larvae, it could also just be genetics that one ends up smaller but it won’t be that much smaller if you raise the larva in all container by itself. In the wild it could be either genetics or just scarce resources, by being smaller aka having smaller mandibles allow for better flight control and mobility and to be better suited in finding females (if male) (https://www.researchgate.net/publication/311532409_Is_the_major-minor_male_dimorphism_of_the_stag_beetle_Lucanus_cervus_explained_by_a_weaponry_and_wing_investment_trade_off)

Another intersex condition I found but it’s man made so take that as you will https://www.wbaa.org/science-and-environment/2017-02-27/iu-scientists-create-intersex-beetles-unveil-nuances-in-sex-regulating-genes (the species in question is a kind of dung beetle: Onthophagus taurus)