It doesn't matter what they wanted to do. What matters is what happened. As a result of their actions they got cut off. If Germany had invaded Ukraine (via Poland?) the gas might still be on. Of course we don't know that because other countries would likely take offense to that action and I'm not willing to predict how the world would change if they had. (I can't even imagine change would cause them to be willing to invade in the first place, much less how everyone else would respond.)

Politics often are about the unintended consequences. Often they are also unforeseen.

Germany joining the Russian invasion was never anything even remotely in the option space at all - utterly inconceivable in 2022. (Not aware of Russia seeking any such support there either.)