Andrey Yermak resigned among corruption scandal. The waves if shitflood reach high.
I read/heard somewhere he was not just a simple right hand man, but a gatekeeper, noone could meet Zelensky without him agreeing on that. I have no source on hand however.
Anyway just the most clueless naive Westerners can be surprised about this. These practices are most common in Eastern Europe. It's not like West isn't corrupt but they stack things differently.
https://www.cbsnews.com/news/zelenskyy-ukraine-corruption-scandal-chief-of-staff-andriy-yermak/