What is the most professional way to fire a toxic client who is paying well but ruining your mental health?

[Btaliat]

It is very difficult to make a move when you have a client that is ready to pay you high but he's very toxic. In fact, it makes it very difficult for the freelancers to make any move. However, it is important for the freelancers to easily make decisions, especially if they want to be taken seriously by the clients and even if they want to ease their mental health. In this scenario, what will be your suggestion?