Within our own solar system that generally means sample return, or sending people with a full biology lab. For an extrasolar planet? I don't think the astrobiology community is of a single mind regarding what should count as direct observation there. We're not sending people or doing sample return for thousands of years. One common opinion I've heard is that seeing an atmospheric spectrograph indicating the presence of biomarkers like oxygen and methane within the habitable zone would be a bio signature, but multi pixel imaging of the planet would be required to claim direct observation. I'm not sure this is a very strong scientific distinction, however.
I'm not an astrobiologist btw, but I used to work at astrobiology.nasa.gov. Small world!
Here is an interesting proposal for direct imaging of an exoplanet with 1 km resolution:
https://arxiv.org/abs/1802.08421
...and an interesting youtube video about it:
I found and read that before my above comment (and skimmed some of the associated paper[1]) but all that says is direct detection hasn't been attempted since Viking, and that most good signals require in situ or sample return.
It still doesn't answer my question! "astrobiologists distinguish between direct detection of life and biosignatures".
The highest methods in terms of strength of evidence obtainable with remote sensing would be finding "deviations from thermodynamic equilibrium and/or kinetics" of "co-located reductant and oxidant" or "element or isotope fractionations indicative of metabolism". Which sound a whole lot like a detection of a biosignature, which "astrobiologists distinguish" from direct detection . :)
I suspect direct detection in an astrobiological context must mean either "direct, as in we physically touched it" or maybe "a signature found using direct imaging".
Definitions are hard. :)
1: https://www.liebertpub.com/doi/full/10.1089/ast.2017.1773