[SPOILER BELOW]
In the Thronebreaker: The Witcher TalesThronebreaker: The Witcher Tales,
Geralt helped Meve, the queen of Lyria and Rivia, to fight the Nilfgaardians. I expect witchers tend to be neutral in wars and don't kill humans unless humans want to kill witchers (except for witchers from some schools such as Viper or Cat). Witchers are trained to slainslay monsters, not humans. Besides, nobody asked Geralt to help Meve although she was outnumbered by the blackclad army. So, why did he helpedhelp her?