As others suggested, take note and proof. Start by copying the exact same content you've published here, and complete it with new toxic behaviour. What will create a body of proofs HR will need and will "expel it" from your head.
I would also meet your manager's manager, this situation has taken too long to resolve and your manager is not doing enough (as far as we know at least). Ask your N+1 whether he has heard of the situation, if he has not your manager is in troubles.
Finally, you have not described how others employees are living through this situation, they may be upset to and be able to help: - they can report the employee behaviour - they can react when the employee is not behaving correctly - they can provide feedbacks, ideas, support?
I wish you all the best, this is a hard situation you're living!