The 2020 Summer Olympics,
officially the Games of the XXXII Olympiad.
en.wikipedia.org
A modern Olympiad refers to a four-year period beginning January 1 of the year the Olympic Summer Games are normally held. The first modern Olympiad began January 1, 1896, the second January 1, 1900, and so on (the 32nd began January 1, 2020: see the Olympic Charter
It doesn't matter what year the actual Summer games are held ... they are still referred to as being the games of a specific Olympiad. (And there is only ONE Summer games held during each Olympiad!)
So on that basis, any player who wins the Olympic Gold in Tennis can achieve the Golden Slam by winning the Grand Slam in any of the years of the Olympiad in which they achieved the Gold Medal
And if you believe that, you probably believe Rios is the GOAT.
Seriously though, a Golden Slam (also known as a Golden Grand Slam), is defined as winning all four Major Titles and the Olympic Gold Medal IN THE SAME CALENDAR YEAR! There is no condition stipulating that the Olympic Games must be conducted in an exact four year cycle, just that only one Summer games is conducted during each Olympiad.