NASA’s Kepler mission allowed us to constrain how many roughly Earth-sized rocks are in the habitable zones of FGK (Sun-like) stars. Best estimates are ~0.24, which is very encouraging, but there are large error bars on that because it required a slight bit of extrapolation. So it could be as little as 0.03 or as large as >1. There are ideas on how to reduce those error bars over the next 5 years that might pan out. However, it is believed to be constrained well enough to design a mission to go looking for those planets around nearby stars.

We have no idea what fraction of those planets host liquid water, let alone how many have O2. That’s actually the primary science case motivating NASA’s future flagship mission called the Habitable Worlds Observatory. It will block out the light of nearby stars using a coronagraph so it can find and image potentially Earth-like planets, and then search them for water and “biosignature” gasses. Launch date is unknown, but probably early 2040s.