Rook I'm wondering if they can confiscate the ships and cargo (if any) if they can prove sabotage?
In one sense, a country can do whatever it can get away with, depending on: its power relative to another nation's power, its internal laws, and any international agreements it's party to. Given that the Baltic is relatively narrow, territorial waters (the "12-mile limit") come into play from a jurisdiction standpoint, as well as various interpretations of national "exclusive economic zones" (which run to 200 miles out). Even the widest areas of the Baltic require ships to transit through 12-mile territorial waters to access them, so countries like Sweden, Denmark, and Germany have degrees of territorial oversight regarding all shipping transits into/out-of the Baltic... hence they can stop and interdict ships deemed to be problematic.
If sabotage is proven, recovering the ships becomes a serious challenge for the nation in which their owners are registered. Cargo confiscation is a different matter, depending on who actually owns it and the nature of the transportation agreement between the shipping company and the listed owner.
The two previously-seized ships related to Baltic cable cuts have now both been released. The Bulgarian ship Vezhen that cut the cable between Latvia and Sweden was boarded on 26 January by Sweden who seized the vessel, but it was later released after they determined the cable cutting was accidental and involved both foul weather and failures of anchor-securing equipment. The Norwegians boarded and seized the all-Russian-crewed Norwegian ship Silver Dania on 31 January after another cut of that cable, but the ship was released on 1 February after a lack of evidence could be found that it had dropped its anchor near the cable cut.
What is of current concern is the sharp increase in the last few months of communication cable cuts in the Baltic (including the power cable cuts), which are running far above that normally experienced worldwide. Given the geopolitical atmosphere (crises in the Ukraine, Sweden/Finland joining NATO, tension between Russia and the West, etc), suspicions naturally reside at a high level. The notable increase in the presence of Russian spy ships and underwater 'exploration' ships in the Baltic has only heightened those fears. Now after a third Baltic cable cutting episode in just a few months (not to mention the 2022 severing of the gas pipelines from Russia to Europe), folks in that region are seriously on edge.