On top of what everybody else has said, I also don't think it's a given, even if/once we crack the technology, that anybody will actually use it to generate power. I think there's a totally plausible outcome where somebody builds a fusion reactor that produces more energy than it consumes and said reactor has essentially infinite, essentially free fuel, but the design they come up with costs $20 billion a pop to build (or whatever) with no clear path to making it cheaper, and just the cost of capital to build new plants makes those plants more expensive per unit of energy generated than coal/gas/solar/etc. even though the fuel costs nothing. At that point, even if it works, maybe the one demonstrator plant they end up building continues to tick away as a singular novelty and the rest of the world carries on building gas plants and solar.

Fission is already in not too different a place than that: fuel is nowhere near the dominant cost per unit of energy produced. I hope that ends up not being the case with fusion, but it's hard to predict at this point.