There is one thing that might point towards Russia blowing up their own pipeline: Before the pipes were destroyed completely, the Russians were coming up with all sorts of strange excuses for why they were reducing the amount of gas delivered through the pipes. Even though it was obvious to everyone that the reductions were for political reasons, the Russians kept insisting that there was force majeure. So its not completely unthinkable that they would blow up their own pipeline just to not have to announce they are stopping sales of gas to europe.
https://www.reuters.com/business/energy/nord-stream-turbine-...