Fission (and likely fusion) ended up being too complicated and expensive to do the job. But renewables appear to be much better situated to push out fossil fuels over the next several decades.
The problem at the moment with renewables is they still don't provide reliable base load, and energy storage systems while useful locally are proving incredibly expensive at scale. The fact is the only option we have right now in many countries for reliable base load generation outside fossil fuels is nuclear. Some other options may eventually become viable, like geothermal or fusion, but there's no realistic prospect of that over the next few decades.
If we want to get serious right now about eliminating fossil fuels, the fact is the answer is a mix of renewables and nuclear.
The "renewables can't supply baseload" has been so well debunked that at this point I have zero respect for anyone (typically nuclear stans) still trotting out that argument. No, renewables damn well can supply baseload, and likely cheaper than fission. The question is exactly which renewable sources and storage technologies will end up being cheapest, not whether they can do it at all.
At this point it's a race against the clock and we're losing it badly. If we can't transition to it before it's too late, then that we could do it in theory isn't worth a whole lot.
If we want to get serious right now about eliminating fossil fuels, the fact is the answer is a mix of renewables and nuclear.