But we don't have that solution yet (see above). That's like hanging on the idea of having nuclear fusion available. Yes, theoretically nice, but until they are practical, we shouldn't count on it.

Yes, theoretically the "waste" of current reactors still has energy to be harvested. But practically we can't use them to a degree where there is no waste afterwards.

For the past decades and sitll ongoing, fission reactors are not clean (also decomissioning them leaves a lot of unusable waste; and they have to be decomissioned at some point).

Also from what I know, extracting the nuclear material from the earth and preparing it for use in a fission reactor is not very environmentally friendly either.

Is nuclear better than coal? Very likely. But it's not clean.

Every atom has energy in it, regardless of whether it is radioactive or not. Radioactiveness just makes it relatively easy to extract that energy. But even then, it's not that simple, not every radioactive material is good for a nuclear reactor. If the fuel absorbs too many neutrons without fission, or produces elements that do, then it can become poison for the reactor. And if it, or the elements it produces, emit very few delayed neutrons and very quickly then it makes it harder to keep the reactor in a sub-critical state (i.e. it makes it harder to not make it explore). Often for these reasons you can't fully use reprocessed fuel, and instead you have to mix it in low percentages with normal fuel. Reprocessed fuel is also harder (thus cost more) to produce since you have to work with highly radioactive materials.