The problem here is, while technically possible, many things were simply washed away some 11,800 years ago. This has the effect of changing silt layer dating but also destruction of much evidence, depending on the location.

Would we even recognize the evidence for what is was if we dis find it? We can't even agree on the age of the Sphinx.

You would need to look for trash heaps and landfills. They would be mostly composed of organic household waste that would decay, but they would contain large quantities of non-organic materials that have no business being where they are.

As a modern example consider expired solar panels. If I remember correctly they are composed of gallium doped silicon wafers and copper wiring supported by an aluminum or plastic frame and shielded from the weather by glass. While an ancient civilization may not have had solar cells they would likely have unusual concentrations of materials such as this.

Also consider potential absences of material where it should be. All around the world there are abandoned mine shafts but I have yet to hear about such a thing that could not be traced to human endeavor.

Personally I do follow the belief that there was previous technical societies as many ancient texts speak of. You can find carvings on rocks that show bicycles and other techs. You can find ooparts from all over the world. Many things fossilize, even metal.

Some excerpts

Faunal radiation and extinctions

The last few centuries have seen significant changes in the abundance and spread of small animals, particularly rats, mice and cats, etc. that are associated with human exploration and biotic exchanges. Isolated populations almost everywhere have now been superseded in many respects by these invasive species. The fossil record will likely indicate a large faunal radiation of these indicator species at this point. [...]

Non-naturally occurring synthetics

There are many chemicals that have been (or were) manufactured industrially that for various reasons can spread and persist in the environment for a long time [...]

Other classes of synthetic biomarkers may also persist in sediments. For instance, steroids, leaf waxes, alkenones and lipids can be preserved in sediment for many millions of years (i.e. Pagani et al., Reference Pagani2006). What might distinguish naturally occurring biomarkers from synthetics might be the chirality of the molecules. Most total synthesis pathways do not discriminate between D- and L-chirality, while biological processes are almost exclusively monochiral (Meierhenrich, Reference Meierhenrich2008) (for instance, naturally occurring amino acids are all L-forms, and almost all sugars are D-forms).

Transuranic elements

Many radioactive isotopes that are related to anthropogenic fission or nuclear arms, have half-lives that are long, but not long enough to be relevant here. However, there are two isotopes that are potentially long-lived enough. Specifically, Plutonium-244 (half-life 80.8 million years) and Curium-247 (half-life 15 million years) would be detectable for a large fraction of the relevant time period if they were deposited in sufficient quantities, say, as a result of a nuclear weapon exchange. There are no known natural sources of 244Pu outside of supernovae.