I'd accept that you are going to pursue getting over the line of the PhD even if it wasn't an ideal fit or your other misgivings about it. It's really just a piece of paper when it is all said and done, and it sounds like it will be a very useful piece of paper since you were in a prestigious group.

Once you've accepted that will happen, you just need to set a simple plan of how to get there in one piece. Make sure you are indeed carving out a little bit of time for things you love doing. When you are depressed that can be very difficult but just think of what you really loved and enjoyed two or five years ago and put it on the calendar, all the better if it is a cheap plane ticket or some other reservation required so you obligate future you to do it. I'd also suggest sending a message to all of those scattered friends to reconnect, easy to do and will help ground yourself.

Finally, do you have any sort of exercise habit? If not seriously consider doing something 3-4x a week for half an hour that gets you sweaty. You don't have to love the activity but it helps if it's fun or just fits into your routine effortlessly.

You are so goddamn young mate. you are going to make it.