No more often than once a month, if that.
Years ago I concocted an oil for my handguns that I have used for nearly fifty years with good success. I blend automotive motor and Three In One machine oil in roughly a 50/50 mix. After cleaning, I oil my gun pretty heavily, then after a minute of so, wipe it down with a blue paper shop towel like those from AutoZone. This keeps the gun well protected yet not too oily.
Motor oil disolves carbon better than most gun cleaning products.