I agree that a state actor was involved.
I disagree that Russia has no incentive.
While the USA obviously has the means and more than zero motivation, I don’t see this type of infrastructure damage so close to allies as likely. Especially given the EU was already in the process of permanently ending the purchase of all Russian gas, not just these pipelines.
Russia, however, is looking at one never-opened pipeline and one already-offline pipeline, which is going to a bloc that has announced that it won’t pay as much as Russia is asking for its gas, won’t pay in the currency Russia is demanding, and wants to rapidly move away from Russian gas entirely, and which is currently sanctioning against Russia. Russia appears to believe that cutting off gas to Europe will end European support for Ukraine, and therefore has an obvious incentive to cut it off. Russia has incentives to make this look like it isn’t Russia’s fault, for the same reason anyone who might have done this would have had an incentive to hide their own identity.