I re-studied how the rankings for the Australian Open works in 2022 and it is ABYSMAL, I will tell you. But before all of that, I want to re-clarify something first: Both Medvedev and Zverev can become number 1 if either one of them wins the AO title, it is a fact. Now, if either one of them does win the AO title, then they can't become number 1 officially until February 21, 2022. I will explain why below
I will try my best to simplify the AWFUL ranking computation for the Australian Open in 2022, by the way, the rankings ONLY applies to the players that played from the 2020 AND 2021, so here it goes:
Scenario 1: If the player has the same result in both 2020 AND 2021
First specific example: Djokovic - he won the titles in 2020 and 2021, but he is not playing in 2022 so he will lose 2,000 points. Now, the question is when he will lose those 2,000 points? The answer is February 21, 2022. The reason for that is because 2021 AO started three weeks later, so because he will have a lower result in 2022 than in 2021, his points won't drop until February 21, 2022.
Basically, Djokovic will be at 11,015 points until February 21st. So, he gets to stay at number 1 for three weeks assuming neither Medvedev nor Zverev does not win the AO title.
The above scenario does not only apply to Djokovic but to the players that will have a lower result in 2022 compared to 2020/2021.
Second specific example: Nadal - he finished QF in both 2020 and 2021. He is actually playing the 2022 AO so he can add points for the weeks of January 31st, 2022 until the week of February 14th, 2022.
Let's say Nadal reached the 4th round and lost in that round, he will then get 180 points added to his ranking:
4875 + 180 points = 5,055 points from January 31st to February 20th
Then, he will lose the 360 points from 2020/2021 AO results on February 21st, therefore his rankings points will be 4,695 points on February 21st.
Scenario 2: If the player had a higher result in 2021 than in 2020
It is basically like the Nadal specific scenario. Let's use Medvedev as an example in this scenario:
If Medvedev wins the AO title, then
8935 + 2,000 points = 10,935 points from January 31st to February 20th
Then, on February 21st, the 2021 AO points will drop therefore, his ranking points will be 9735 (will still be higher than Djokovic at this date).
*He will actually drop 500 points from last year's ATP Cup (2021) so if he wins the AO title, then he will be at 9,235 and Djokovic will be at 8,875 because he will also drop points from last year's ATP Cup.*
Last scenario: If the player had a higher result in 2020 than in 2021
I will use Zverev as a primary example in this scenario. His scenario is different than the first two scenarios.
He is actually truly defending his points, therefore if he does loses points, then the points will drop on January 31st NOT on February 21st. The good thing though is that Zverev is not defending 720 points (2020 results), but he is only defending the difference between 2020 AND 2021 results, therefore he is only defending 360 points in 2022. In this case, he can gain HUGE amount of points OR lose SMALL amount of points.
If Zverev wins the AO title then
7,970 (before the Australian Open 2022) - 370 points (the difference between his 2020 and 2021 results) + 2000 points = 9,600 points
Those 9,600 points will be official on January 31st and no points will be dropped on February 21st due to Zverev having a higher 2020 results than 2021.