It takes only 5 years to build a nuclear power plant, (…)
I agree with most of the comment, but this is just an oversimplification. I’m sure that you can build a nuclear power plant in 5 years, if you have the requisite infrastructure, engineers and knowledge. Germany did not have any of those in sufficient amount to build anywhere near enough nuclear reactors between the decision to switch to coal & gas in around 2011 and the full-scale Russian invasion of Ukraine in 2022. Even France wouldn’t be capable of that in such a short amount of time.
Had they made that decision 30 years ago, sure, but in such short time? No way.