The evidence would be enormous.
Such a civilization wouldn't just spring up out of nowhere, going instantly from the Stone Age to 21st Century (at least) technology. It would take thousands of years and a population base of at least hundreds of millions of people. Such a civilization would leave worldwide evidence.
A trivial example: glass bottles, when buried, can last essentially unchanged for hundreds of thousands of years.
Another example: the amount of metal used in a modern city would leave traces in the soil and rock that could still be detected millions of years later. Even if your hypothetical city recycled to an extent that would make environmental activists giddy with joy, they still would have had cities in their past that didn't have the technology to do so.
If there had been a highly technological civilization prior to 10,000 years ago, we would have found traces (and more) of it by now.
The older cities would be mined for the metals, and the remaining traces after enough weathering could easily be taken as ore deposits.
Yes, there should be hard evidence, and yes, there are many OOPArts out there, and yes, we do try very hard to fit them into our current world view, or they get filed and forgotten.
Keep in mind that I am speculating, not advocating the certainty of an antediluvian society, but merely allowing the possibility that one could have existed, as yet undiscovered and/or unrecognized.
A post collapse religious fervor could even have gone to great efforts to eliminate every trace of any previous technology or civilization, no library of Alexandria, no statue of Buddha is immune.