Owning a property is not a job but maintaining one can be. If you don’t own the property then that’d just be called being a janitor.
Janitors are cleaners. Typically the people who maintain apartments are called maintenance workers, handymen, or (old fashioned) superintendent. Sometimes property manager, if they also handle renting it out.
Definition of janitor:
one who keeps the premises of a building (such as an apartment or office) clean, tends the heating system, and makes minor repairs
https://www.merriam-webster.com/dictionary/janitor
a person employed to take care of a large building, such as a school, and who deals with the cleaning, repairs, etc.
Or
a person whose job is to clean and take care of a building
Janitors are only employed in large, expensive apartment buildings. Single family homes don’t use them, nor do cheaper apartments. So that’s not really descriptive of a landlords job at all.