>>8911889
99.99999999 °C

But more seriously, water could remain liquid under sufficient pressure, so a heavy atmosphere/high gravity. Phase diagram suggests that the highest possible temperature where water could remain liquid is about 370 °C, but this would require over 200 times the atmospheric pressure of Earth. You'd also need much more stable biomolecules with a higher temperature.

I think something like a planet with a reflective atmosphere that allows it to stay much closer to the sun with Earth-like conditions. Could work by the atmosphere having a lot of airborne particulates with high albedo, but that brings its own set of problems.