Each horse is different and will bring their own quirks to the mix, but generally, same sex groups do better, have less strife.
A mare and gelding can become overly attached, generally the gelding, the mare may not care.
Have friends that kept mixed herds and did say, they had more injuries, but for them it was worth managing them all in one group.
We always kept them separate and rarely had any injuries over many decades, broodmares and riding mares in one, geldings and one stallion in the other…
Whatever horses you get, you will never know how they will get along until you try them together.
Even horses that get along for years, one day something will set them off and have some big differences, to us humans seemingly out of the blue some times.
That is horses for you.