So what 'group' sympatheic to Ukraine has the capacity to do this? Well, from Wiki...
Like all post-Soviet states, Ukraine inherited its special forces (Spetsnaz) units from the remnants of the Soviet armed forces, GRU and KGB units. Ukraine now maintains its own Spetsnaz structure under the control of the Ministry of Internal Affairs and under the Ministry of Defence, while the Security Service of Ukraine maintains its own Spetsnaz force, the Alpha group. In 2016 the Special Operations Forces were created as an independent branch of the Armed Forces of Ukraine formed only by special forces units.
It so happens that among other units, the Ukrainians have the 1st Underwater demolitions Unit of the 73rd Naval Special Purpose Center, Ochakiv. So while we, myself included, have assumed that Ukraine did not have the capacity to do this, now I am not so sure they could not have. Its relatively easy to move around Europe so its not a stretch to see special operators from Ukraine making it to the Baltic.
If it is Ukraine, it was a risky move. They hurt the Russian economy through reduced cash flow, but could upset the very NATO countries they need support from. So you wouldn't expect them to admit to it.
That's not an argument. woke, neocon idiots in Washington DC specialize in that. And they've just made their biggest blunder yet.
Keep in mind that Germany has existed for hundreds of years without Russian Gas. Germany is making do.
Russia on the other hand is withering with the loss of all income but especially the sales of gas and oil. As time goes by the withering worstens. Russia has tried to remedy the situation but in geeral has failed. The inability to deliver severely restricts sales. The delivery by tanker is badly hampered by the fact that many of the tankers are sanctioned and thus un available. Further, Turkey has closed the egress from the Black Sea to tankers lacking proper marine insurance. All the reputable insurers have sanctioned Russia.
So, all in all, the result is bad news for Putin