I did something similiar once. I had personal problems with my project manager, and he was also one of the reasons I left. Could that be the case for you? But because everybody else knew, everybody else could prepare, and I actively managed knowledge transfer, so the rest of the team wouldn't suffer. Even my department head was informed, so he had the chance to search for a replacement.

You have given no other indication of their behavior, or why it should be destabilising. If this person is otherwise behaving professionally, so doesn't bad mouth the company or anything like that and the only difference is that this person puts in the minimum amount of required effort, a lot of people will understand that you dont go above and beyond anymore when you leave. So just treat the situation professionaly and act like you knew nothing, while preparing for the departure.

If there is any specific bad behavior, focus your actions on that. Apart from that, just prepare to the best of your ability.

I did something similar once. I had personal problems with my project manager, and he was also one of the reasons I left. Could that be the case for you? But because everybody else knew, everybody else could prepare, and I actively managed knowledge transfer, so the rest of the team wouldn't suffer. Even my department head was informed, so he had the chance to search for a replacement.

You have given no other indication of their behavior, or why it should be destabilising. If this person is otherwise behaving professionally, i.e. doesn't bad mouth the company or anything like that and the only difference is that this person puts in the minimum amount of required effort, a lot of people will understand that you don't go above and beyond anymore when you leave. So just treat the situation professionally and act like you knew nothing, while preparing for the departure.

If there is any specific bad behavior, focus your actions on that. Apart from that, just prepare to the best of your ability.