It is not about "fossil fuel or nuclear". Fossil fuel has few (and fewer and fewer) advocates. it is about "renewable or nuclear", and the trend is clear:

https://ourworldindata.org/grapher/nuclear-renewables-electr...

... even in the most heavily nuclearized nation: https://ourworldindata.org/grapher/electricity-fossil-renewa...

... even in the most touted nuclear-leading nation: https://ourworldindata.org/grapher/electricity-fossil-renewa...