Norway, Denmark, Sweden, and Poland stand to benefit the most due to their new Baltic Pipeline so they seem to be the most likely to have sabotaged the pipelines. The Baltic Pipe officially became operational on 27 September 2022,[1] one day after a series of as of yet unexplained explosions on 26 September 2022 rendered the competing Nord Stream 1 and Nord Stream 2 pipelines from Russia to Germany inoperable.[2] Thus, it seems those 4 countries are the most motivated to sabotage the Nordstream pipelines.

[1] https://www.regjeringen.no/en/aktuelt/opening-of-baltic-pipe...

[2] https://abcnews.go.com/International/wireStory/germany-press...