[matteocantiello]

Yes, I agree with the point that Oxygen is not answering the question definitively. The issue is that say, you build a very, very expensive space telescope and you have to decide if you want it to look for Oxygen or CFC. CFC is a shot in the dark: likely you won't see anything (see my previous comment). Which means likely no data, no PhD thesis, nothing. You pretty much wasted a few billion dollars and you're not ruling out much because what if civilizations only use chemical energy sources for ~200 yrs, then they all switch to nuclear fusion? On the other hand is likely Oxygen will show up as a signature in some exoplanets, and a lot of new understanding about exoplanet atmosphere and geology would follow. Which, among many other things, might help us narrowing down planets where to look for life and how. And next iteration of instruments we might be able to really discover life. So this is why review panels do opt for choices that are more likely to benefit the scientific community at large. It might sound a bit incremental at first, but it's how progress is made. This said, it's not like astrophysicists are not thinking about detecting technosignatures in exoplanetary spectra, see e.g. 3.2 in https://www.liebertpub.com/doi/10.1089/ast.2009.0371 and e.g. https://elib.dlr.de/119683/1/1803.05179.pdf