That report is from 2020. Costs have fallen greatly since then, particularly for battery storage. And even so, that report doesn't say fossil fuels are needed (although the "net zero" solution still is allowed to burn some, I'm guessing because CO2 absorbed into the oceans isn't being counted?) It even says explicitly that hydrogen would be used for long term storage! See pages 5 and 6.
With hydrogen available renewables can straightforwardly get to 100%. Germany has plenty of geology for hydrogen storage. As I mentioned elsewhere, long term thermal storage is also a possibility, with recent developments there suggesting very competitive capex.
If not, grow that industry. Just like one would have to do with nuclear if one were to adopt that technology. You do realize that existing burner reactors cannot power the world for more than a few decades, right? The available cheap uranium runs out. Breeder reactors are not commercially available, or available at a cost competitive even with existing commercial burner reactors.
(The French have given up on their breeder development program, cancelling Astrid, the proposed next project, until at least 2050.)
Renewables and storage seem much more quickly scalable than nuclear, as demonstrated by the yearly percentage rate of increase in their deployment.
France generally export quite large amounts of electricity. But whenever a cold spell hits that export flow is reversed to imports and they have to start up local fossil gas and coal based production.
What they have done is that they have outsourced the management of their grid to their neighbors and rely on 35 GW of fossil based electricity production both inside France and their neighbors grids. Because France's nuclear power produces too much when no one wants the electricity and too little when it is actually needed.
Their neighbors are able to both absorb the cold spell which very likely hits them as well, their own grid as the French exports stops and they start exporting to France.
I'm not aware of that, because it's a lie. Storage is another alternative.