And I am sorry to say but the many countries have made great strides on running their countries on more and more renewable energy sources.
In 2018, Scotland generated 98% their energy from wind alone.
Denmark 72%, Germany 45%, Uruguay 97%, Norway 93%.
It's a whole patchwork of solutions, depending on geography.
Nuclear is not this magic bullet, and just means flipping a switch, it has a major cost, logistical, technological and risk overhead associated with it. If you are France, great, but they have been doing Nuclear since the beginning, it doesn't mean that the world has to do the same, when far simpler, cheaper and safer alternatives are in abundance.
Usual fluctuations (eg. no photovoltaic by night, more wind in the afternoon) can be planned for, but local events such as big clouds or no wind are frequent but have a great impact on
Germany is doing Sektorenkopplung, so attempting to switch everything over to electricity.
This is done because electricity is more efficient and we will use less total energy for the same effect. E.g. a heatpump can make available 3-5 times it's consumption of electricity as heat, where a gas stove can only reach 1.
Until we have found ways to drastically cut down power usage AND to store huge quantities of energy OR found another similar and cleaner and safer energy source, we will need it in the mix to balance with other renewable sources.