That depends on what you mean by biology-based tech, afterall, we're also a civilization deeply rooted in biology-based tech. It's not necessarily the case tha

That depends on what you mean by biology-based tech, afterall, we're also a civilization deeply rooted in biology-based tech. It's not necessarily the case that all organic materials are ephemeral over these timespans. Assuming that a tool-using civilization would have needs covering a wide range of material properties, including high corrosion resistance, there is no reason why even biologically-grown building materials would automatically be less durable than, say, concrete. Not to mention the tools and trinkets of everyday life. The assumption is that a large population always has a large footprint regarding the traces it leaves behind, even if that footprint is very different from ours. We found this to be true in fossils that have been left behind even by exceptionally fragile creatures. Once we're talking advanced biology-based tech, this becomes even more pronounced. Outright genetic engineering in Earth's past would be bound to leave very curious traces in lifeforms that are around today. In fact, if I wanted to leave a message behind for a hypothetical civilization located on this planet a million years into the future, leaving it in DNA would be one of the very few viable choices. I would posit that even DRMed biotech designed to turn every single piece of a civilization into mud once the license runs out would leave behind very detectable traces in the form of strange geological deposits and individual artifacts that survived against all odds.