Can you point me to a country-scale implementation of solar+batteries where electricity is affordable? If every country tries to do the same, what do you think will happen with the battery costs given the sheer size of the manufacturing and natural ressources extraction required?

California, while not a country, is basically the size of one and they have made significant progress with this strategy.

Why is this any different than the sheer size of manufacturing and natural resources to extract other forms of energy?

Oil, natural gas, coal also all take vast amounts of capital investment and resource extraction to implement.

I think that a nuclear power plant is vastly more efficient on this aspect.

And California has the most expensive electricity prices in the US.

https://www.electricchoice.com/electricity-prices-by-state/