Bad politicians ask people how they should do a thing, then do that thing.
It's been awhile since Germany has had good politicians where energy is concerned.
Then they did away with a big component of "Plan A" in nuclear after Fukushima, which promoted Russian gas to an essential component of their transition energy mix.
At the end of the day, if Germany hadn't stopped building nuclear or decommissioned reactors, Ukraine probably wouldn't have been invaded.
Russia surely nudged, but if Germany hadn't already been trending in that direction then it wouldn't have stuck.
Putin invaded Ukraine because he wanted to, and Germany had nothing to do with that.
The belief that Germany would rather sacrifice Ukraine than lose Russian gas would have been less plausible if 30% nuclear energy had been retained.
Russia didn't make a rational decision: we know that Putin hid the plan from most of his subordinates, ignored concerns presented by the rest, and the system withheld important facts from him likewise. He made a huge gamble with his "3-day special operation".
Also, the nuclear plants would have provided only a partial backup for the Russian gas, as electricity from the plants couldn't replace the direct use of gas in German houses and industry anyway.
A bad one, because their facts were wrong, but one based off calculations rather than rolling dice:
+ Russian Cold War-era (and refits of same) military materiel is reaching obsolescence and end of life. Russia can't afford to modernize its military at scale (hence the obsession with announcing prototype superweapons)
+ US and European ties are at a low point, as a consequence of the Trump presidency
+ US is focused on China as a peer threat
+ Germany is uniquely diplomatically vulnerable to gas energy pressure, but only until additional renewables come online, transmission infrastructure is upgraded, and efficiency measures implemented (see the Nord Stream bombing whodoneit https://en.m.wikipedia.org/wiki/2022_Nord_Stream_pipeline_sa... )
+ Remaining ex-Warsaw Pact / non-NATO countries are likely accede to NATO in the next few years (see https://en.m.wikipedia.org/wiki/Enlargement_of_NATO#Current_... )
... ergo, there was no better time to make the attempt than now. Everyone just assumed Putin wouldn't be stupid enough to try.
But that calculation looks very different without the energy vulnerability, as Russia understands the economic difference between themselves and Germany.