Won’t the Vera Rubin Telescope (formerly LSST) settle this? It’s going to observe the entire night sky every few nights and provide enough data to find nearby moving objects.
I buy a lot of my telescope equipment from Celestron so I got their kit. It was like $2 more than the knockoff brands but I like my eyeballs so went with a company I trust with relatively inexpensive optics.
It’s a good biosignature but a real smoking gun would be if a planet has intelligent life that’s not always so intelligent. Then, we might detect chlorofluorocarbons or some other synthetic pollutant.
“Well, we detected an alien civilization but their atmosphere is in way worse shape than 1950’s London and they’re 100 light years away. I guess we’ll keep checking and see if they get their act together or not.”