Again. Nobody is saying there is a definitive starting point of “In the year 0 ICBA, the first homo sapien was born”. There fundamentally cannot be without omnipotence.

But… there was. Or, to be less precise, there were probably multiple definitive starting points before one took hold.

You can have an individual born that appeared strikingly like a modern human, but if their population hasn’t genetically changed enough their offspring go right back to looking just like any other precursor to modern humans.

Yes. The individual was, potentially, “evolved”. But the population “reverted” back. That doesn’t change the fact that there was an individual who had reached the next stage. Because… a mutation/defect is isolated until it isn’t.

But for the purposes of a thought experiment/“shower thought”? Yeah, there was very much a point where a single human existed. We just will never know beyond “it probably happened in this very large span of time”.

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Which is actually how most science works. You cannot ever know what the first molecule in a rockslide to start moving was (without, again, omnipotence). But you can decrease the granularity and understand what the first rock to fall or even what part of the rock tipped over first and so forth.

For all scientific and “meaningful” purposes? That is sufficient and it is just not worth even discussing which molecule “started it”.

For the purposes of philosophy and thought experiments? There was very much a first molecule. It just doesn’t matter outside of that domain.