Easy to imagine a motive for Russia, if you don't imagine it as a unitary block. Some inside the wealthy elite want to go back to the pre-war status quo, where they get to make $$$ selling fossil fuels to Europe. By blowing up NordStream, you do something like Viking raiders burning bridges behind them; it tells everyone on your side there's no going back, it's victory or death. If some of Russia's elite think they could be getting $$$ a month after a peace deal, they might be pushing for a quick end by withdrawing back to 2014 (or even 1991) line of control, which might work for them but not for Putin.

Now none of this means it actually was Russia, I don't claim to know any better than anyone else. But there was certainly a motive (for some in) Russia to want NordStream out of the way.