Its an exciting time to be alive because as of recently we certainly can detect planetary atmosphere major components out to at least 700 or so light years.
https://en.wikipedia.org/wiki/WASP-39b
There are astronomers actively working on minor component, more biologically interesting spectrographs like chlorophyll rather than spectrograms of carbon dioxide. That'll be harder to detect and limited to shorter ranges.
At some point, probably very soon, like less than a decade, we'll be able to definitively state that we have atmospheric data in an onion layer shaped shell where we have unequivocable proof that out to X lightyears from Earth there's no planetary scale chlorophyll higher than a minimal level aka there's no earth-like plants on that planet. That shell will likely expand over time. Or, perhaps we will find a forested, or at least algae covered, planet, some light years away, which would be very interesting indeed.
The question is rapidly changing from a purely philosophical belief to scientific observation, like right now, in real time, in the 2020s. What a cool time to be alive!
This follows old, old stuff from radio astronomy along the lines of how far away could a 1960s radio telescope realistically detect life on earth. The answer IIRC was not very far LOL. But there's been a lot of progress in radio astronomy, etc.
With respect to fermi filters etc people need to pay attention to how far away the Earth can be detected using radio telescopes. That distance has imploded since the end of analog UHF TV broadcasts. We still broadcast absolute swill, in fact more than ever, but digital detection range is much lower than analog AM carrier detection range from analog TV. The Earth has, to some extent, recently gone radio-quiet, which is interesting because we are still here, in fact more of us than ever. So WRT fermi filters of not being able to detect civilizations, disappearance of 1950s/1960s signals does not necessarily imply disappearance of civilization. Another example, if any aliens are watching the high altitude freon contamination of our atmosphere they're likely really confused right about now.