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The oldest known undisturbed area of the Earth's surface is only about 2 million years old

It turns over very fast in geological time

https://www.livescience.com/3542-oldest-surface-earth-discov...

A fair point. I wasn't thinking about tectonic subduction, which would hide pretty much all evidence that anyone was there. Though I think that article is talking more about having the same surface exposed to the air for a long time, without being worn down by weathering or covered in silt. You could have an area covered in dirt or partly eroded away, and still be recognizably an artifact of civilization for a long time. I don't know if such things would last billions of years though.

Also, I expect weathering and erosion would happen a lot faster on Venus, what with the high heat and extreme winds that are more like a flowing ocean current than what we'd think of as "wind".

Have a look at the Silurian Hypothesis. If one can examine things very closely, literally on the ground, then the window of detectability might extend to hundreds of millions of years, even billions perhaps. But from orbit, there's not so much hope of detection after a million years

And yet we have fossils from half a billion years ago. "Oldest surface" is not a good measure for how long evidence can survive.

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