> they've been wanting to get that pipeline approved and operational
Not recently. Recently, they pulled out a string of excuses to send less and less gas over (turbine bing repaired, sanctions, etc.) to show Europe their leverage. They don't feel any lack of money currently, and they know with current hydrocarbon prices, they have options to sell, even if at discount, and no money shortages currently. So they're betting on European population being weak and European energy infrastructure being dependent on Russian hydrocarbons, and thus citizens pushing the politicians to make nice with Russia.
The fact that they invested a lot of money in it means nothing. They have money. They have oil and gas that they can sell for money. What they need is for the West not to send so much weapons and ammunition to Ukraine that Russian army, numerous but weak and disorganized, will be completely crushed and expelled from Ukraine. Cutting off the flow directly would expose them to contractual sanctions, which can be leveraged against assets Russia still has in the West. But cutting off the flow by "mysterious explosion" reaches the same goal while providing Russians with tiny veiled plausible deniability. That's how they always operate. I'm sure in 5 years or so they'd admit it openly. Just as they admitted that "insurgents" in East Ukraine and Crimea were actually Russian military and intelligence officers, or Putin's private military "Wagner Group" exists, was created by a close Putin ally - which they were denying for years - and is operating in Ukraine.