While I wouldn't discount the ability of Ukrainian divers to pull off an operation to destroy the pipelines, a lot of people forget about the actual issues the Nord Stream line was having during the summer of 2022 before the explosions. Only one of the two Nord Stream lines was in use because there was only one functional compressor, and even that line was taken offline for maintenance a few times leading to some wild spikes in Euro gas futures in August. There was an available replacement that had been sent to Canada for maintenance but it was held up due to sanctions and was unlikely to ever be released given the war in Ukraine.
My personal theory has always been that Russia blew up 3 out of the 4 pipes in an attempt to force Germany to approve transit on the undamaged and entirely functional Nord Stream 2 line. Russia figured the parts they had available for both Nord Stream 1 lines were failing or had failed and the line would be unviable soon anyways. Why not try to force Germany's hand by making one of the functional but unused Nord Stream 2 lines the only available option, with all the parts from the other, damaged, NS 2 line available as spares. Then sow as much disinfo as possible to confuse who did it. Volumes would be roughly equal or even a little more through NS2-B than what they were supplying in summer '22 through the single NS1 line and Russia expected prices to remain elevated a lot more so than they did.
Reuters article from August 22 regarding compressor issues https://www.reuters.com/business/energy/gazprom-says-nord-stream-1-pipeline-shut-three-days-end-aug-2022-08-19/
And then less than two weeks after the Nord Stream explosions, here's Putin saying oh by the way we can still send you guys gas through the one pipe that's left https://www.reuters.com/world/europe/putin-moots-major-gas-hub-turkey-with-nord-stream-supplies-2022-10-12/