“The Oxygen Bottleneck for Technospheres”, Amedeo Balbi, Adam Frank2023-08-02 (science, tech)⁠:

On Earth, the development of technology required easy access to open air combustion, which is only possible when oxygen partial pressure, P(O₂), is above 18%.

This suggests that only planets with atmospheric oxygen concentrations will be capable of developing “advanced” technospheres and hence detectable techno-signatures.