Depends on your goals and how much weight you have to lose, right?
1000 kcal/day is certainly doable, especially if you have a lot of weight to lose. But it’s hard, it sucks, and you would have to engineer your workouts around this. I think SSB 2 would be really rough on that big a deficit. Maybe SSB 1 low volume, adding aerobic rides as you can, or traditional base. I did about that big a deficit, with IF and a lot of Z2 biking, for about half a year. Had to stop eventually, but I stopped about 25 kg lighter.