Is it permissible to mention the injustices of the ex-spouse when asked about the reason for divorce, or is that considered backbiting? And is it sufficient to say "we didn't get along"?

Backbiting is forbidden, as Allah Almighty says: "And do not backbite each other." An exception to this is the oppressed person who complains about their oppressor, as Allah Almighty says: "Allah does not like the public mention of evil except by one who has been wronged." Therefore, you are permitted to speak of the injustice your ex-husband inflicted upon you by way of seeking redress.