Both, I would imagine.
It’s hard to tell how custom would have evolved, and there’s no one grand way that ‘matriarchal society’ would work.
But, for one, I would imagine that in a society where women have traditionally been in more control of their bodies and their sexual desires, and where women are not infantilized or shunted into positions of societal weakness, I feel like there would be less of the issues surrounding men being compromised emotionally or ~sexually~ by serving in the field with female comrades that so many people in our day and age claim is/would/will be an issue? So very likely there could be a much more systemically equal spread of gender.
However, in terms of how men tend to be physically stronger than women, I would be interested in seeing a military structure wherein men form the squadrons, the footsoldiers, the cavalry, the black-ops teams, while women serve in more powerful, strategic roles such as the higher officer ranks and squadron leaders.
It would be very cool, for example, to see a system where the officers are performative warrior-priestesses, garbed in pearl epaulettes and sweeping rich military uniforms, highly trained both physically and mentally and held in high respect bordering on awe/worship by the lower ranked men.
There comes with this a lot of class struggle issues and it’s bordering on just-for-kicks-misandry if done wrong, but in terms of actual military structure and psychology it could be really fascinating and, if nothing else, aesthetically provocative, as most things are when war gets performative.