The suffix at the end of that last name is also causing some trouble:
In Ukrainian, it’s Зеленський (note the “ь”, a silent letter supposed to soften the consonant before itself)
In Russian, it’s Зеленский (no “ь”, the “н” is not soft)
In Polish, it’s Zełenski (no “й” or anything similar, resulting in a different pronunciation again)
Now compare it to the last name of a Polish author: Сапковський (Ukrainian), Сапковский (Russian), Sapkowski (Polish).
Ukrainians, Russians, and Poles all have examples of last names like these, but the rules of our languages dictate that we handle them differently, even in terms of spelling and pronunciation; for people not speaking a Slavic language naturally, it understandably is a nightmare, as neither spelling is objectively the right one in terms of linguistics.
For now, it’s probably best to either go with one of the following:
Zelensky or Zelenski, akin to Polish equivalent spelling of similar last names
Zelenskyy, as seems to be the more or less official or judicial spelling of this Ukrainian last name
As messy as it seems, I believe it’s going to stay the same. Romanization of the Russian language is already an equally messy phenomenon despite multiple efforts to standardize the process, yet it only resulted in several ways of tackling the difficult cases, which is of very little help; Ukrainian seems to be an even more complicated case for romanization as it has some features that would either require intricate rules to create accurate spellings, or make greater use of diacritics.