How can I help my ex get out of his toxic relationship without coming across as wanting him back?

mmmm this is hard one.... perhaps you could ask him to meet you as a friend and talk to him like a friend without coming across as interfering. You could say " look i can see you have been a bit unhappy lately is there anything you need to talk about" if he doesnt want to talk to pry him just accept it and just talk to him normally as a friend...thats probably ideally what he needs right now.. as he is stuck in what you say is a toxic relationship. but you cant force him to talk if he doesnt want to..thats his decision just let him know what your always there if he needs someone to talk to...as an outsider looking in from a distance.