By now there have been many reports of this type of crash where after one ends their turn it reaches a faction number then the game proceeds to freeze and after a few seconds crashes, the game closes.
I too have had it recently with The Empire at turn 58 it crashed on an undiscoverd faction's turn (124). I have even tried to reload a save from 4 turns before and play differently but it still crashed at exactly the same turn and exactly the same faction.
so now that you have received quite a number of these reports, when will you fix it? XD
like...it's a famous bug now, if you go to total war discord and say the "end turn crash" bug people instantly know what it is