We couldn't have stopped using fossil fuels heavily until nuclear power was widespread and implemented, around the late 70s or 80s.
We could have traditioned our grids off of fossil fuels but we also depend on them for fertilizer to feed the world and for transportation which, until very recently, didn't have a viable alternative.
Nuclear was also kneecapped by FUD and astroturfing, and we didn't properly fund renewables because Republican administrations were in the pockets of big oil. Did you know GM made a fully viable electric car that people loved back in the 90s? Setback after setback, all self-inflicted, people pretending we have these insurmountable hurdles all over the place. Pathetic for an empire that prides itself as a champion of industry.
The fertilizer thing is a perfect example. We don't need to extract, refine, and burn nearly as much fuel as we do to get the fertilizer we need. People make the same empty argument about the cheap plastic shit that dominates the economy as if the world didn't exist before cheap plastic shit and couldn't exist after.