The atmosphere have ~1 atm pressure at sea level, It does have water ocean maybe 10-30% of the surface, also it supports tectonic plates so the carbon cycle does work, and the Ocean is made mainly of H2O with traces of H2CO3 since it will absorb some CO2, The day is ~42 hours so will cause a lot of water to evaporate.
So based on that: I thought of this atmosphere: 89.5% N2 1-2% H2O 1-3% CO2 2-5% argon (CO2 and Argon changeable choose any percentage for them) 0.5% other gases
Is it plausible with Earth-like temperature? if no how could a planet lose its CO2 and how could it support an H2O ocean with no problems, and will it be safe for the human skin? so u could walk there with just an Oxygen mask?