is there a way to change the voting system from FPTP winner takes all to like proportional or rcv or something?
Currently there is no way to change it yourself. Some districts will have a cultural trait that will cause the seats in that district to be distributed according to proportional representation or a majority bonus system instead of winner takes it all.
I'll look into if I can add an option to set the default seat distribution method in the custom game setup, might be an interesting alternative game mode/setting.